Shopping for a notebook involves a delicate balance between battery life, performance, usability, and price. No two users share the exact same criteria for what they consider the right blend. That’s why we try to evaluate mobile platforms based on their perceived strengths. Take last year's Netbook Buyer’s Guide as an example. We considered the fact that some buyers are willing to spend more for battery life and forgo a bit of performance. Others are willing to pay an extra $100 or $150 to get both. Another group cares more about usability. The list of ways to break even this one specific market into tiny pieces goes on and on.
Credit: Jake Edmonson
If battery life is your number one priority, shopping choices are limited. Clearly, there are notebooks designed for those on the move. But what if you don't want to sacrifice elsewhere to get that mobility? Maybe you just need another hour of run time to get your current notebook through the day. If that's the case, a brand new system doesn't make much sense.
Even if you already own a notebook that delivers ample battery life, we're certain that there are travel days when even a power-sipping system just doesn't have enough juice to last through closing time. If you spend a lot of time on the road, layovers don’t provide enough time at an AC jack to get you back to 100%. That might mean your in-flight entertainment gets interrupted right before the big climax. Sleeping, talking to unwilling neighbors, and hitting on flight attendants only eats so much time. What other options are there?
There is a solution, though. Check out an extended laptop battery, which comes in the form of an even larger installed battery pack compatible with your existing system. There is a big catch. These batteries (often denser six-cell or nine-cell) weigh down your machine, altering its mobile profile. These batteries stick out the backside of your notebook like a sore thumb, and can turn a sleek thin and light notebook into a clunky desktop replacement.
Fortunately, there is another option, too: universal extended batteries. These batteries don’t plug into your system directly. Instead, they function similar to uninterruptible power supplies (UPS), which we often associate with safeguarding desktops. They are always external units, but often have a small profile that makes them easier to pack for travel, offering higher densities than extended batteries can't provide. And if that wasn't enough, you generally get the ability to charge your cell phone, iPod, and camera from them as well.
After we published our Netbook Buyer’s Guide, one reader posed a question about mobility in the comments. So, during the past two months, we hunted down just about every available solution capable of extending the battery life of your notebook. If you're on the go, this story is for you.
We are listing the total capacity of the batteries here, but we want to point out this isn't always an apples-to-apples comparison. mAh is the SI abbreviation for milliampere-hour. This is a quick and dirty way to compare the relative energy stored in one battery to that of another. However, these comparisons are only useful if you are looking at same battery chemistry.
If you want to think of capacity as how much fuel the battery holds, like a tank of gas, then chemistry is the type of fuel. If you are comparing lithium-ion polymer to nickel-metal hydride batteries, you might as well be talking about diesel and gas-powered cars. Also, think of the huge energy difference between one pound of coal and one pound of uranium. So, the only real metric of a battery's utility is to measure how long it actually runs. In lieu of automobiles and miles per gallon, our benchmark lab tests notebooks and battery life.
| Brand | Amstar | Amstar | Brunton | Brunton | Digipower |
|---|---|---|---|---|---|
| Model | MedXP 140 | MedXP 300 | Sustain | Impel | Universal Laptop Battery |
| Chemistry | Lithium-Ion Prismatic | Lithium-Ion Cylindrical | Lithium Polymer | Lithium Polymer | Lithium-Ion |
| Output Rating | - | - | 60 Wh (19 V @ 3.2 Ah) | 60 Wh (19 V @ 3.2 Ah) | - |
| Battery Rating | - | - | - | - | 4400 mAh |
| Battery Capacity | 140 Wh | 293.04 Wh (14.8 V @ 19.8 Ah) | 73 Wh | 146 Wh | 48.8 Wh (11.1 V @ 4.4 Ah) |
| LCD | N | Y | N | N | N |
| Battery Guage | Y | Y | Y | Y | Y |
| Output Cable Length | 6' | 6' | 34" | 34" | 30" |
| Output Voltages | 16, 20 | 12, 16, 19, 24 | 12, 16, 19 | 12, 16, 19 | 16, 19 |
| Charger (Watts) | 90 | 130 | 38 | 38 | 28 |
| Charger Weight | 0.86 | 1.58 | 0.41 | 0.41 | 0.58 |
| USB ports | N | 1 | 1 | 1 | 1 |
| Casing | Aluminum & Rubber | ABS Plastic | Rubberized plastic | Rubberized plastic | Aluminum & ABS plastic |
| Length | 10.38" | 10.75" | 7.25" | 7.75" | 6.5" |
| Width | 8.63" | 7.38" | 6.75" | 3.75" | 3.25" |
| Height | .56" | 1.63" | 1.13" | 1.13" | 1" |
| Weight (lbs) | 3.4 | 5.38 | 2.38 | 1.31 | 1.13 |
| Warranty (years) | 6 months | 6 months | 1 | 1 | 1 |
| Warranty on cells | 6 months | 6 months | 1 | 1 | 1 |
| Warranty registration | N | N | N | N | N |
| Brand | Electrovaya | Electrovaya | Energizer | Energizer | Lenmar |
|---|---|---|---|---|---|
| Model | PowerPad 95 | PowerPad 130 | XP8000 | XP18000 | PPU916 |
| Chemistry | SuperPolymer Lithium-Ion | SuperPolymer Lithium-Ion | Lithium Polymer | Lithium Polymer | Lithium Polymer |
| Output Rating | - | - | 38 Wh (19 V @ 2.0 Ah) | 66.5 Wh (19 V @ 3.5 Ah) | - |
| Battery Rating | - | - | 8000 mAh | 18 000 mAh | - |
| Battery Capacity | 95 Wh (15 V @ 6.3 Ah) | 130 Wh (15 V @ 8.6 Ah) | - | - | 104.5 Wh (19 V @ 5.5 Ah) |
| LCD | LCM | LCM | N | N | N |
| Battery Guage | Y | Y | Y | Y | Y |
| Output Cable Length | 27" | 27" | 26.5" (9 V-12 V), 26.5" (16 V-20 V) | 26.5" (9 V-12 V), 26.5" (16 V-20 V) | 29.5" |
| Output Voltages | 15, 16, 18, 18, 19, 20, 24 | 15, 16, 18, 18, 19, 20, 24 | 9-12, 16-20 | 9-12, 16-20 | 16, 19 |
| Charger (Watts) | - | - | 60 | 65 | - |
| Charger Weight | - | - | 0.72 | 0.65 | - |
| USB ports | 2 | 2 | 1 | 1 | 1 |
| Casing | ABS plastic | ABS plastic | ABS plastic | ABS plastic | Aluminum |
| Length | 10.63" | 10.63" | 4.38" | 7.13" | 7.25" |
| Width | 8.25" | 8.25" | 2.88" | 4.88" | 4.94" |
| Height | .69" | .69" | .94" | .81" | .56" |
| Weight (lbs) | 2.02 | 2.38 | 0.49 | 1.11 | 1.15 |
| Warranty (years) | 1 | 1 | 3 | 3 | 1 |
| Warranty on cells | 1 | 1 | 6 months | 6 months | 1 |
| Warranty registration | N | N | Required | Required | N |
| Brand | PowerTraveller | PowerTraveller | Tekkeon | Tekkeon | Tekkeon |
|---|---|---|---|---|---|
| Model | MiniGorilla | PowerGorilla | MP3750 | MP3450 | MP3450i |
| Chemistry | Lithium Polymer | Lithium Polymer | Lithium Polymer | Lithium Polymer | Lithium Polymer |
| Output Rating | 38 Wh (19 V @ 2.0 Ah) | 104.5 Wh (19 V @ 5.5 Ah) | 49.4 Wh (19 V @ 2.6 Ah) | 49.4 Wh (19 V @ 2.6 Ah) | 57 Wh (19 V @ 3.0 Ah) |
| Battery Rating | 9000 mAh | 21 000 mAh | - | - | - |
| Battery Capacity | - | - | - | - | - |
| LCD | Y | Y | N | N | N |
| Battery Guage | Y | Y | Y | Y | Y |
| Output Cable Length | 32" | 32" | 26" | 26" | 26" |
| Output Voltages | 8.4, 9.5, 10.5, 12, 19 | 8.4, 9.5, 12, 16, 19, 24 | 10, 12, 14, 16, 18, 19 | 5, 6, 7.5, 9, 12, 14, 16, 19 | 5, 5.5, 6, 6.5, 7.5, 8.4, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19 |
| Charger (Watts) | 12 | 37 | - | 60 | 60 |
| Charger Weight | 0.25 | 0.34 | - | 0.87 | 0.86 |
| USB ports | 1 | 1 | 1 | 1 | 1 |
| Casing | Rubberized ABS Plastic | Aluminum & Rubber | ABS plastic | ABS plastic | ABS plastic |
| Length | 5.94" | 8.5" | 6.88" | 6.88" | 6.88" |
| Width | 3.25" | 5.25" | 3.31" | 3.31" | 3.31" |
| Height | .63" | .69" | .94" | .94" | .94" |
| Weight (lbs) | 0.59 | 1.43 | 0.93 | 0.94 | 0.95 |
| Warranty (years) | 1 | 1 | 1 | 1 | 1 |
| Warranty on cells | 1 | 1 | 1 | 1 | 1 |
| Warranty registration | Required | Required | Required | Required | Required |
Inside Your Laptop: Power Distribution
Remember your desktop system? The power supply has 5 V, 3.3 V, and 12 V power rails. Those exist on your mobile system as well. But on a notebook, the power brick doesn't deliver those three voltages to the motherboard, as a PSU does. Instead, the brick delivers a steady voltage to your notebook's input connector. After that, voltage regulators on the laptop motherboard do the rest of the work to output voltages that the CPU, graphics processor, storage and add-in cards can use.
Displays are a different beast altogether. Older CCFL LCD panels need a voltage higher than what your notebook’s power supply can deliver. In order to achieve that higher voltage, a component called a power inverter is used to convert back to a low-frequency AC current. The existing generation of notebooks use LED-based LCD panels, which don't have this high voltage requirement, as they are solid-state devices. Instead, LED backlights operate off of +5 or +12 VDC. LEDs use less power than CCFL backlights; additionally, the lack of a power inverter translates into better efficiency as well.
How does the battery all tie in? The battery supplies power to the input side of the regulators, just like power coming from the wall socket would if you connected that way. However, there is a separate charging circuit. This diverts power from the AC adapter before it gets to the voltage regulators so that your battery charges. This charging circuit is the reason why the voltage on the AC adapter is always rated higher than the one stamped on the battery. You need a higher voltage to charge your battery.
Extended batteries are unlike the battery that ships with your notebook. The most obvious difference is that they come with a variety of tips, since they claim universality with each manufacturer's specific power connector.
Tip Set from Duracell's Universal Adapter
Even within a single brand, it is possible to find notebooks that use different voltages or plug sizes. For example, Dell has a standard plug size, but the Inspiron Minis are exceptions to this rule.
The stock power adapter that ships with your notebook supplies voltage at a fixed setting. This is not so for the external batteries. In order to deliver the multiple voltages required by different devices, they must also be capable of outputting different voltages.

There are a couple of ways to do this. The easiest way is to use a voltage converter controlled with a manual switch. Some companies choose to go a step further by using a sense resistor in the adapter tip. The sense resistor drops the voltage as current crosses its path. The small voltage drops are fed to a simple comparator circuit, which is then used to control the VDC output from the power supply.
If the resistor is in the tip, there is an additional layer of protection because you cannot force an incorrect voltage over a plug. Physical switches give you more control, but there is a chance that you'll choose an incorrect voltage and damage your notebook.
The way voltage gets to your notebook is important to understanding how an external battery can affect run time. Say your internal laptop battery yields two hours and your external battery offers an additional two hours. If your notebook is at 50% and your external battery is at 100%, this doesn't mean you get three hours total. There is an efficiency loss involved whenever you make an energy transfer, and you see this happen whenever the external battery charges the internal battery. This ineffiiency is less than what you see with an AC to DC conversion if you were to use a UPS, but it is there all the same. Remember that this only applies during a transfer of energy from battery to battery. If your notebook was at 100% and external battery was at 50%, you would see three hours total.
First up, we have the MedXP 140 and 300 from Amstron. These two models are the upper-end of the company's external battery lineup. There is a MedXP 66, but this wasn't available to us for testing. These are the two heaviest batteries in our roundup, and that heft is each to see in their durable construction.
The MedXP 140 is encased in aluminum with a rubber bumper. Comparatively, the behemoth-sized MedXP 300 is encased in a very thick ~1/8" shell of what seems to be ABS plastic. Both come with a full set of tips for a wide range of laptop vendors. However, only the MedXP 300 has a USB port for charging smaller devices.
These two external batteries are intended for industrial applications, particularly in the medical field. Amstron envisions its products placed on medical carts to drive mobile computers, which hospital staff can use to interact with other medical equipment.
Because of the large capacity of its batteries, Amstron provides beefy AC adapters to charge them.
Using these devices is easy. Just select the correct tip and you're good to go. The only major complaint we have is that the angled plug on the MedXP 140 makes it hard to charge without removing the output cable. The MedXP 300's charger plug is on the other side of the unit, so there is no plug conflict. Ideally, both batteries would have an off state, but this only exists on the MedXP 300.
If you are an avid outdoorsman (or outdoorswoman), than you are already familiar with Bruton. It sells a lot of its camping products through REI. But the company also makes solar- and battery-based products. If you want a battery specifically designed for use outdoors, Bruton’s Sustain and Impel are the way to go. Both are encased in a thick shell of ABS and rubberized plastic.
These are the only batteries in our roundup that are water resistant. For all other batteries in our roundup, water will void your warranty. This doesn’t mean you take a Bruton battery underwater, but it does mean exposure to rainwater, white water rafting, and occasional splashes at the beach are all permissible. Because water may cause a short circuit, the company provides a pin to reset the tripped circuit.
Each battery comes with a charger, output cable, and seven tips. Notice that one of the tips is on a slightly longer extension. This cable is used specifically for Dell notebooks that use the PA-12 charger. Just plug a tip into the output cable, connect it to the battery, hook it up to a notebook, and press the On button (default state is off). While there is a degree of overvolt protection, these batteries do not use sense resistors. You must correctly select the right voltage or you could potentially harm your notebook.
Digipower's Universal Notebook Battery was a bit hard to track down for several reasons. Digipower is a brand of Mizco Electronics, and our inquiries to the company initially went unanswered. To expedite the process, we pulled this unit from Amazon. As a roundup, this story should reflect the full range of available buying options.
Unfortunately, our initial battery pack turned out to be a dud after one week into testing, which we chalked up to an anomaly. We tried to contact Digipower directly, but there is no phone number listed on its Web site. Furthermore, we submitted multiple messages via the company's comment form that went unanswered.
After tracking down the parent company's head office, we ran into even more issues. We were informed that Digipower wasn't interested in press (whoops) because its products weren't intended for the US market. Instead, it sells into overseas markets like China. The representative promptly informed us that she would hang up within three seconds and requested no further contact. As we were trying to explain our situation, we heard an immediate click. Subsequent efforts to contact the company were unsuccessful.
As a result, we can't really say if we ran into a bad batch from Digipower, or if the company's products are simply as terrible as its customer service. We did try another unit from Amazon, but ran into the same issues. According to a user-based Amazon review, we aren't the only ones experiencing problems with Digipower's Universal Notebook Battery. It just doesn't hold a charge at all beyond the one-week mark.
Unfortunately for Digipower, not only is it actually selling products in the United States, but we're also a global organization reviewing hardware for multiple countries. We take issues with the company's belief that it can ignore press. Good products are good products and bad products are bad products. Until we experience otherwise, this is a bad product supported by a manufacturer that seems to know it's selling garbage.
For the purposes of our quantitative measurements, we're excluding the results of this product due to the limited number of available test runs before it ceased working entirely. This is really unfortunate. The build quality of the aluminum shell is actually pretty good: solid, durable, and with smooth lines. The only thing we didn't like was the On/Off button, which seems to stick and has little to no tactile feedback.
Electrovaya and APC were the two of the first companies to make external batteries. While APC has since discontinued the Universal Notebook Battery, Electrovaya still considers external batteries a staple business product, and counts hospitals and IT staff among its most frequent customers.
There are only two battery models: the PowerPad 95 and 130, named after their watt-hour ratings. Encased in a thick shell of hard ABS plastic, the PowerPad's batteries can take a fair deal of punishment.
Electrovaya uses a prorpriety lithium-ion chemistry called lithium-ion SuperPolymer, which claims a longer battery life than the typical lithium-lon seen in your notebook.
Electrovaya tells us it hasn't dropped the PowerPad 95 from its lineup. But that unit has been out of stock much longer than the 130, so we hope this is just a short-term supply problem. Both products have two USB ports to charge your cellphone and other peripherals, along with a LCD that shows the current status of the battery.
The fuel gauge recently underwent a firmware revision, which is why the information on Electrovaya’s Web site is slightly out of date. Previously, the fuel gauge was a digital counter.

The company switched to an icon, which sections off the remaining charge in 20% increments. We asked Electrovaya to explain the change, and it cited an updated firmware that includes further power saving enhancements. These improvements added enough code that Electrovaya was required to remove existing portions of the old firmware to fit it on the same ROM. Personally, the digital counter was one of the things I loved about the PowerPads, so it's disappointing to see that feature removed. It is our hope that Electrovaya physically implements a larger memory chip moving forward so we don’t have to give up one benefit to get another.
Most batteries have no easy way to check degradation (the ability to hold a charge). The PowerPads cleverly show this information under SoH or “State of Health.” This small line tells you how much of the originally battery life you can still reach. For example, if you were originally getting 10 hours and now are getting 9 hours, the meter would read 90%.

Using a PowerPad is easy. The single button under the LCD is more than just an On/Off switch. Once you plug in a tip, the sense resistor has a feedback loop that causes a processor in the PowerPad to recognize the voltage. You must press the button on the confirmation screen in order for the battery to start outputting current. This is Electrovaya’s second line of defense to prevent damage.
Most batteries require their own charger, but PowerPads can use the same charger as your notebook. How can that be? Because different notebooks charge at different voltages, so do the PowerPads. They use sense resistors on the input side as well as the output side. So, what happens if you use a 16 V input tip and a 19 V output? In that case, you charge the PowerPad battery, but you can't output power to the notebook. This is a safety mechanism that Electrovaya implemented to prevent electrical failure. The entire circuit must operate on the same voltage or power output will be disabled.
The above picture showcases the entire input/output tip set. However, PowerPads are the only batteries included in our roundup that don't include a starter set of tips. Each input/output tip runs $10. You get a discount for buying the whole set, but you probably won't need that wide range of compatibility options unless you are in an IT department.
Energizer is a brand we all know. However, these batteries are not actually made by Energizer. The pink bunny company has its own factories that produce standard-cell batteries. These external notebook products actually come from a separate company. Energizer licensed its brand to TennRich, which is headquartered in Taiwan. XPal Power is a California-based subsidiary of TennRich, which actually produces all the Energizer "Energi To Go" power packs.
XP18000 | XP8000 |
While the company sells many power-oriented products, there are only two external battery solutions that work with notebooks: the XP8000 and the XP18000. The XP8000 is strictly meant for netbooks. If you have anything beyond a netbook, you'd want to get the XP18000.
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The only difference between the two units is the swapped position of the USB and charging port.
Neither battery has a voltage switch. Energizer chose a design that uses sense resistors to correctly output voltage. However, unlike other batteries, there are two power rails. The green cable outputs 9 V-12 V for devices like cellphones, while the blue cable outputs 16 V-20 V, depending on your notebook. Energizer's batteries operate in a live state all of the time. So, to power your notebook, just plug in the tip.
Oddly, the 65 W charger for the XP18000 is smaller than the 60 W charger for the XP8000. The two adapters are sourced from different companies, and this is a difference we expect to see in retail units. As we understand it, the 65 W charger for the XP18000 was separately qualified to meet the higher charging requirements.
Lenmar's PPU1619 was one of the first external battery solutions that turned up on Amazon during our virtual shopping trip. It's incredibly similar, in our opinion, to the older Tekkeon myPower batteries.
The company more recently released its PPU916, which looks remarkably different. It is housed in a brushed aluminum shell, and the form factor is small, compact, and rectangular. Its shape alone is a plus because it easily fits into a briefcase pocket.
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Connectivity is straightforward. You only have to deal with a single input and output port. Voltage is manually selected, but is limited to two voltages (16 and 19 V).
Lenmar takes a different approach to charging, like Electrovaya. Instead of using a discrete charger specifically for the PPU916, you use your notebook's charger, along with one of the input tips (right-angled plugs).

The only issue we ran into was a typo in the company's manual. It states that all five LEDs on the unit are used to indicate charge level, and the fifth LED serves two purposes: indicating 80%-100% and also functioning as the charging indicator.

When we actually looked at the unit, it turned out that the fifth LED is not dual-purpose. This means the scale is actually in 25% percent increments, instead of 20%.
Straight out of the UK, we have PowerTraveler’s PowerGorilla and MiniGorilla. I’m not sure about the motivation behind this company’s fascination with primates, as most of its products are named after gorillas or monkeys, but PowerTraveler is trying to aim its products toward folks living an active lifestyle.
Both batteries employ a rugged design, similar to those from Bruton. There are some differences, though. We'd argue that the PowerGorilla was built with less impact resistance in mind.
PowerTraveller saddled rubber bumpers on the sides of both batteries, but only the MiniGorilla is encased in rubberized plastic. Meanwhile, the PowerGorilla is housed in an aluminum shell.
Besides Electryovaya’s PowerPads, the PowerGorilla and MiniGorilla are the only other batteries in this roundup to use an LCD. But disappointingly, this battery gauge is a bar meter. The LCD clearly wasn’t designed with the meter in mind. Instead, it provides a way for you to select the correct voltage. If your notebook is already connected, simply hit the On/Off button to cycle through the options. Once you get to a compatible voltage, the battery detects the current drain and blinks to indicate its locked selection.
I discovered this can be a faulty process. Some notebooks trickle drain off of a 16 V charge. If this happens, the battery mistakenly locks into a voltage that doesn’t charge or power your notebook. You need to unplug the external battery pack and cycle manually through to the correct voltage before you plug it in.
Both batteries charge at 16 V with the included chargers, but only the PowerGorilla comes with a set of right-angled input tips, which allows you to charge using your notebook’s stock adapter. With that said, both batteries feature the most complete set of accessories seen in this roundup. The US plug is compatible in Japan and Canada by default, but PowerTraveller also includes the UK and Australia/Europe adapters as well.
The last three batteries in our roundup come from Tekkeon. While the company offers many portable power solutions, these are the only products that can be used to power your notebook.
The myPower batteries aren’t really designed to take a lot of abuse. Their ABS plastic cases aren't thin, but they will crack if you drop them on a hard surface. More annoyingly, these are the only batteries in the roundup (besides those from Energizer) that use a high-gloss black piano finish. I’m not against this type of design, but it isn't very suitable for high-mobility devices.
The bottom half of the battery is matte to begin with, so it wouldn’t be too much of a stretch to use that motif for the whole design.

The purposes of these three batteries can be a bit confusing. All of them are suitable for use with notebooks. There isn’t a netbook- or notebook-specific model, but the MP3750 is the only one that comes with the tips necessary for use with full-sized notebooks like the Vostro 3300 and ThinkPad T510. For that reason, we exclude the MP3450 and MP3450i from our notebook battery test.

The MP3450 and MP3450i can also be used with notebooks, but their compatibility lists are shorter. Instead, those two models are better suited to portable DVD players and digital cameras.
The MP3450i, in particular, allows more granular control through the use of DIP switches. This is a feature you won’t see on the MP3450 or MP3750. Moreover, voltages listed in the table only apply to voltages supported through the output cable. All three batteries still output 5 V through the USB port.
All three batteries have eight LEDs, and the first indicates On/Off status. The MP3750 employs a different design than the other two, though. When you plug a tip into the connected output cable, the battery has no off status. Instead, it is either in a manual or auto voltage selection mode. The MP3750's second LED indicates whether you are in manual mode, while the first indicates auto. It is the only battery to feature an auto-selection mode.
Choosing this option causes the battery to use a sense resistor to ratchet up voltage until the notebook starts to draw power. Once that occurs, the battery locks in the voltage. In manual mode, you need to cycle to the correct voltage using the button above the LEDs before you hook the external battery to your notebook.
You use a Mac, then you know that everything got a little more complicated with the MagSafe connector. There are very few ways to get an external battery to work with your MacBook. One roundabout way is to output 12 V to a cigarette adapter and use Apple’s Airline MagSafe adapter. Only the PowerGorilla and XP18000 support that option, but the cigarette adapter is separate purchase in the case of the XP18000.
There is a big problem with this suggestion, though. The current Airline MagSafe connector doesn’t actually step up the voltage. It just delivers 12 V to the computer, which is enough to keep the notebook alive. Unfortunately, it isn't enough to charge the battery. In fact, it doesn’t even really fully power the larger 15.6" and 17.3" MacBook Pros. The larger systems switch from 16 V to 19 V during heavier workloads, so you'd only really slow down the rate of discharge.
Apple is the only major notebook vendor that supplies a branded non-charging auto option, which makes this somewhat of an anomaly. Some people have resorted to modifying the Airline MagSafe adapter, but it doesn't come with a charging circuit. No amount of modification is going to solve your charging problem.
There are options coming from HyperMac (HyperJuice looks interesting) and QuickerTek. Trouble started a few months back when Apple claimed that HyperMac was manufacturing cables with MagSafe connectors, violating the Cupertino-based company's patent.
Meanwhile, there was Mike Lee of MikeGyver, plugging along. Before MagSafe was even a blip on the radar, Mike made mods for PowerBooks. Apples employees even use his kits because he warranties his work. Mike actually cuts a MagSafe cable off of a retail Apple power adapter and modifies the input end to accept the 16 V plug used by the last generation of IBM ThinkPads. This simple adjustment allows you to charge your MBP, provided you have his modified cable and an adapter that can output to the old 16 V ThinkPad tip. This is completely legal because it's not a counterfeit Apple product. It is simply a mod, and selling a mod is legal under the principle of first use.
There is a downside to this, though. You must use either use a modified Apple power adapter from MikeGyver or switch over to a third-party power adapter.
You can attempt to do this yourself, as others have, but it's an involved process. The elastic sheath on the cable makes it hard to modify, since you need to always keep it taut and straightened out. If you are willing to supply your own adapter, or if you have a custom setup requirement, Mike usually just charges the labor fee for modifying the plug.
Modified Auto/Air MagSafe Adapter by Stuart Schmitt
There are a number of quirks associated with this approach, but the point is that it works. In fact, we have tried it on new 13.3" MacBook Pro using all of the batteries in our roundup. It works without flaw.
If you are going to attempt to do this yourself, you need to be careful. One of the criticisms of the MagSafe design is that the contacts are too small for the the charging current. Furthermore, the magnet used in the connector attracts iron filings and other ferromagnetic materials. Just Google "MagSafe fire." After creating your own cable, your MagSafe plug may be dirty from its time in the lab. Play it safe and clean up the plug. You can do this with candle wax.
- Drip candle wax onto a surface.
- Knead it until it is just slightly warm and malleable.
- Press it against the MagSafe connector. The wax will pick up any filings or ferromagnetic dust.
- Wipe down the MagSafe connector with a soft cloth to get rid of the wax.
Do not put the MagSafe connector in contact with hot wax. Only do this after it has cooled. A magnet will lose part of its magnetic force when it comes into contact with heat (100 °C). You can also use masking tape, but warm wax is the surest way to get rid of even the smallest filings.
| Test Hardware | ||
|---|---|---|
| Processors | Intel Atom N450 (1.66 GHz) | Intel Core i3-350M (Dual-Core, 2.26 GHz) |
| Memory | 1 GB DDR2-667 | 4 GB DDR3-1066 |
| Graphics | Intel GMA 3150 Broadcom Crystal HD (disabled) | Intel HD Graphics |
| Notebook | Inspiron Mini 10 (1012) | Dell Vostro 3300 |
| Adobe Flash Player | 10.1.102.64 | |
| Operating System | Windows 7 Starter | Windows 7 Professional 64-bit |
| Graphics Driver | 8.14.10.2117 | 8. 14.10.2226 |
There is a long back-story to the battery life benchmark used in this review, which we'll save for some other time. What you should know is that it is similar to BAPCo’s MobileMark, but it differs in a few ways. Like MobileMark, it is a workload-based benchmark, running processes through several programs. However, this is a benchmark that I have coded from scratch, so that is where the similarity ends.
We want to stress real-world usage, which is perhaps one of the biggest reasons we decided to have at an in-house-developed benchmark. This benchmark mimics what you should expect from everyday life. Right now, I have programmed the battery life metric to simulate a user typing at ~45 WPM and reading at ~200 WPM. So, this is a “Real Life Use” benchmark, hence the name: RLUMark (at least until I think of a better name).
Since we are testing netbooks, there is no need to include content creation programs like those from the Adobe CS5 suite. This limits benchmarking to the General Use Battery Workload.
This workload consists of the following programs
- IE8
- Excel 2010
- Word 2010
- Outlook 2010
- WMP12
We will try and keep the benchmark as up to date as possible. Right now, everything has been made current up to 11/20/2010.
In addition, we are always going to benchmark systems as they ship, including their default battery profiles. There is no clean wipe of the OS. In real life, when you buy a notebook, system vendors rarely include a blank copy of Windows 7. Some of the included software is useless, such as trial software, but others programs are important for functionality, for example, ThinkVantage’s Power Manager.
Beyond turning down all the “special offers” when starting the system for the first time and installing Office 2010 Professional Plus, we do not disable or uninstall any software. Bloatware will naturally hog more system resources during the benchmark process, so we want to encourage manufacturers to cut down on this trend. I want to make a point that the time it takes to complete a benchmark workload is unaffected by included software.
Test Conditions for All Systems:
- Windows 7, all patches updated to 11/20/2010
- BIOS updates, current as of 11/20/2010
- Master Audio Volume: 50%
- System Drivers, current as of 11/20/2010
- Graphic Drivers, current as of 11/20/2010
- GMA 3150: 8.14.10.2117
- Intel HD Graphics: 8. 14.10.2226
Some vendors tweak their Windows 7 battery settings a bit in order to maximize battery life and longevity. There isn’t anything wrong with this. Every company has a different battery strategy that it believes is the best for its system. For example, some notebooks are hardwired to force hibernation at 5%. Other systems will let you go all the way to 0% and just die, no matter what you set in the battery profile. We are going to be testing at default shipping settings under the “Balanced” battery profile.
Some manufacturers have a different name for this profile, but this will always be the “Recommended” Windows 7 profile. To simulate the same visual experience, we only “untweak” the display settings to retail Window 7 settings. In addition, all displays have been set to maximum brightness, which is roughly 200 nits for both notebooks. I specifically choose max brightness over the standard 100 nits because most people tend to use the highest brightness setting. Our previous standard of 100 nits applies only to notebook reviews, because we need to standardize the brightness setting across multiple systems.

We expected Amstron's MedXP 300 to lead the pack. Its sheer size suggests lots of battery life. But notice just how far ahead it scores.
Besides the obvious, we have a couple of surprises. Notice that Brunton's Sustain has an output rating of 60 Wh, but comes out ahead of the three ~100 Wh batteries: XP18000, PowerGorilla, and PPU916. This just goes to show that the manufacturer's stated capacity isn't the final word. Voltage and current levels the company uses to test also matter.

Our updated benchmark generates a platform average design power of 11.5 W for the Dell Inspiron Mini 10. We used this value to normalize the capacity of all the batteries tested.


Even though we normalized battery capacity, that doesn't take weight into account. We weighed all of the batteries and graphed capacity and minutes per pound. Similar to normalized battery capacity and battery life, our per-pound metric presents the same data using different units.
While our calculations include the weight of a battery's physical shell, the graph take us by surprise. Pound for pound, Energizer's XP18000 and XP8000 deliver the most battery life. Meanwhile, many of the solutions geared toward industrial use (and consequently employ more durable enclosures) fall to the bottom, including the PowerPad 95 and MedXP 140. Obviously, making a robust battery means using thick armor to protect the battery cells from damage.
The Energizer batteries are the stand-outs here. Compare them to Tekkeon's batteries, which do worse in battery life and have a poorer weight efficiency.

We added a full-sized notebook test because different batteries are designed with different current loads in mind. Our Vostro 3300 uses 3.34 A, compared to the Mini 10's 1.58 A. As our benchmark shows, when you double the load, you basically halve the battery life.

Our updated benchmark generates an average platform design power of 28.2 W For the Dell Vostro 3300. We used this value to normalize the capacity of all batteries tested.


If you take a look at Electrovaya's PowerPad 130, it only comes in second to the XP18000. If the PowerPad had successfully completely all of its test runs in our netbook test, this what we would have seen.
We did not include Tekkeon's MP3450 and MP3450i in the Vostro 3300 test because both lack the necessary tips. The MiniGorilla and XP8000 have similarly been excluded because both are meant specifically for netbooks.
| Charge Time, HH:MM | Stock Adapter | Dell 30 W Adapter | Dell 65 W Adapter | Lenovo 65 W Adapter | Lenovo 90 W Adapter |
|---|---|---|---|---|---|
| Amstron MedXP 140 | 4:50 | - | - | - | - |
| Amstron MedXP 300 | 6:45 | - | - | - | - |
| Brunton Impel | greater than 10 hours | - | - | - | - |
| Brunton Sustain | 6:00 | - | - | - | - |
| Digipower Universal Notebook Battery | N/A | N/A | N/A | N/A | N/A |
| Electrovaya PowerPad 130 | - | - | 3:30 | 3:30 | 3:30 |
| Electrovaya PowerPad 95 | - | - | 3:15 | 3:45 | 3:15 |
| Energizer XP18000 | 2:30 | - | - | - | - |
| Enirgizer XP8000 | 2:35 | - | - | - | - |
| Lenmar PPU916 | - | 4:00 | 4:00 | 4:00 | 4:00 |
| PowerTraveller MiniGorilla | 4:30 | - | - | - | - |
| PowerTraveller PowerGorilla | 4:55 | - | - | - | - |
| Tekkeon MP3450i | 3:30 | - | - | - | - |
| Tekkeon MP3450 | 3:30 | - | - | - | - |
| Tekkeon MP3750 | - | 4:40 | bent pin, unable to test | 3:45 | 3:15 |
We set up a camera to record a time-lapsed video using a five minute shutter interval, and our results are a bit surprising.
Not only does the XP18000 give you the most battery life per pound, but it also charges the fastest.
Remember, charging times are a double-edged sword. Ideally, you want a nice slow charge so that your battery lasts more than a few hundred cycles. Fast charge times get you back away from the wall socket faster. But in the long run, they cut down on the health of the battery.
Brunton implements the most conservative charging scheme, but this solution may make more sense if you are considering pairing it with one of the company's solar panels for a trickle charge.
| Feature Checklist | Dual Charging | Separate Charger | Charges Dell | Charges Mac with MikeGyver MagSafe |
|---|---|---|---|---|
| Amstron MedXP 140 | Y | Y | N | Y |
| Amstron MedXP 300 | Y | Y | N | Y |
| Brunton Impel | N | Y | Y | Y |
| Brunton Sustain | N | Y | Y | Y |
| Digipower Universal Notebook Battery | N/A | Y | N/A | N/A |
| Electrovaya PowerPad 130 | Y | Y | Y | Y |
| Electrovaya PowerPad 95 | Y | Y | Y | Y |
| Energizer XP18000 | Y | Y | N | Y |
| Energizer XP8000 | Y | Y | N | Y |
| Lenmar PPU916 | N | N | N | Y |
| PowerTraveller MiniGorilla | N | Y | N | Y |
| PowerTraveller PowerGorilla | N | Optional | N | Y |
| Tekkeon MP3450 | Y | Y | N | Y |
| Tekkeon MP3450i | Y | N | N | Y |
| Tekkeon MP3750 | Y | Y | N | Y |
| Feature Checklist | Accepts MikeGyver Charger | Use Dissimilar Input/Output Tip Combination | Off state | Linear Battery Gauge |
|---|---|---|---|---|
| Amstron MedXP 140 | N | N/A | N | Y |
| Amstron MedXP 300 | N | N/A | Y | N |
| Brunton Impel | N | N/A | Y | Y |
| Brunton Sustain | N | N/A | Y | Y |
| Digipower Universal Notebook Battery | N/A | N/A | N/A | N/A |
| Electrovaya PowerPad 130 | Y | N | Y | Y |
| Electrovaya PowerPad 95 | Y | N | Y | Y |
| Energizer XP18000 | N/A | N/A | N | Y |
| Energizer XP8000 | N/A | N/A | N | Y |
| Lenmar PPU916 | Y | N/A | N | Y |
| PowerTraveller MiniGorilla | N/A | N | Y | N |
| PowerTraveller PowerGorilla | N | N/A | Y | N |
| Tekkeon MP3450 | N/A | N/A | Y | N |
| Tekkeon MP3450i | N | N | Y | N |
| Tekkeon MP3750 | N/A | N/A | Y | N |
Dual Charging: If your external battery and notebook are both short of a full charge, you need to charge both batteries. If they are connected, the external battery always takes priority. Some batteries will charge both systems at the same time by demanding a higher current from the wall socket. Notice that only a handful of the batteries in this roundup are capable of this.
In the case of Brunton and PowerTraveller, you need to physically disconnect the AC charging cable before using the external battery to power the notebook. The battery refuses to output power otherwise. In the case of Lenmar, you don’t need to disconnect, but everything is done on a priority-based system. Say your notebook is at 50% and the PPU916 is at 90%. First, the PPU916 finishes charging, then it stops charging and charges your notebook. After the PPU916 goes to 0% or your notebook hits 100% (whichever occurs first), it repeats the process. Obviously, Lenmar's implementation is very inefficient. It doesn't properly shunt power.
Separate Charger: Not all of these batteries allow you to make dual use of your notebook’s charger. Some require you to use the one included in the box. Only the PowerGorilla provides an option to choose. Remember that this benefit is a double-edged sword. With a separate charger, you are guaranteed a way to charge your battery. An input tip system has no guarantee unless the company explicitly states that your notebook is compatible.
Charges Dell Notebooks: The majority of Dell notebooks (excluding the Minis) have a power circuit that requires a proprietary identification signal before charging initiates. If this signal is absent, you can only power the notebook. That is why third-party chargers often do not work with Dell notebooks. Some vendors have figured out Dell’s charging scheme and others haven’t. The only batteries in our roundup that can actually charge a Dell notebook are from Electrovaya and Brunton. Every other battery could not charge our Vostro 3300.
Charges Mac with MikeGyver MagSafe: All of these batteries will output to the old 16 V ThinkPad tip. Every battery in our roundup will power and charge a Mac notebook provided you have a modified MagSafe cable.
Accepts MikeGyver’s Charger: MikeGyver’s modified MagSafe charger uses the old 16 V IBM ThinkPad tip. This setup only works with the Electrovaya’s PowerPads and Lenmar’s PPU916. Why? Well, technically Apple’s power brick sends out three voltages. The default is 12 V, which is enough to keeps your Mac powered. That is why the MagSafe’s LED turns green when you first plug it in. When the notebook needs to charge, it demands 16 V (or 19 V if you have a 15.6” or 17.3” MacBook). This demand initiates a voltage switch in the adapter. Electrovaya’s tip system is based on sense resistors, so it demands 16 V from the beginning. The PowerGorilla and MP3750 also use sense resistors, but because the resistor is set up on the input side within the battery, both only detect the default voltage (12 V). This is insufficient to charge either battery. Lenmar doesn’t use sense resistors, but it does have a manual switch that forces the battery into a 16 or 19 V mode. This allows the PPU916 to demand a voltage higher than 12 V from the power brick. The solution is to move to a third-party power brick like Targus' Premium Laptop Charger (APM69US).
Use Dissimilar Input/Output Tip Combination: This is a safety issue. In order to prevent overload (or underload), the entire circuit must maintain the same voltage. This only applies to Electrovaya’s PowerPads, because they allow you to use a notebook’s charger for dual charging. Simply put, you cannot use a 16 V IBM adapter to charge and power a 19 V Dell notebook. If you force this, the PowerPad will refuse to output power until you disconnect the input power source.
Off State: Using a multimeter, I found that only some of these batteries have what would be considered an off state. Even if it has an on/off power state, there is no guarantee that the battery is completely powered down. The lowest state for some of these batteries is similar to the ACPI S3 state. Simply put, the circuit is nearly always live in a kind of sleep state. The difference is minor, but having an off state is important if you want to put these batteries into storage. If we don’t consider chemistry, the ones with a S1-like power state would exhibit the slowest rate of energy leak.
Linear Battery Gauge: Electrovaya no longer uses a digital battery counter. So, all battery gauges are incremental, using bars in an LCD display or multiple LEDs. I have read the manuals to confirm, but several of these batteries have an odd number of indicators or a number that isn't a factor of 10. This means the first LED may indicate a 0-5% charge while the second indicates 5-20%. This is a feature to keep in mind if you need to keep track of how much charge you have left.
Unless the vendor specifically says it supports your notebook, you should double-check with tech support before your purchase. If you have a business notebook from HP, Dell, or Lenovo, you are pretty much in the clear, but we recommend that you check anyway. Some companies are better than others at maintaining a compatibility list. Others don’t publish a compatibility list at all, or only choose to include a list with the product.

There is a fast way to check compatibility. Look up a replacement power adapter with Google. The adapter should be compatible with multiple models. So long as one of the systems matches up to the compatibility lists maintained by each batter vendor, you should be good to go.
So that you don’t have to hunt down compatibility info, we've assembled a list for you to check against. Keep in mind that even if your model isn't listed or confirmed, any external battery will work if it outputs the correct voltage and has a plug that fits.
Amstron: There is a compatibility guide listed on the company’s home page. Amstron also includes a rather extensive compatibility list with its batteries: scanned PDF.
Brunton: There is no current compatibility list published either on the Web site or included with its products. Please contact the company to verify your notebook model.
Digipower: Only the older EBP-NB44 is listed as a current product on the company’s Web site. EBP-NB60 is not listed. Digipower only includes a limited compatibility list with its new battery: scanned PDF.
Electrovaya: The company maintains a current list of supported notebooks. Because tips are a separate purchase, the company encourages customers to contact it before purchase.
Energizer: This is the only brand that maintains a “free tips” service. You get two free tips per year, but you still have to pay for shipping ($3.95 per shipment). XPal maintains one of the most exhaustive databases and even compiles a list on eReader, GPS, and tablet compatibility.
Lenmar: Even though it is fairly out of date, Lenmar publishes a compatibility list on its Web site. We did notice that none of the new Vostros are listed. Seems about one generation behind.
PowerTraveller: The company hosts an online compatibility guide, but it is about half a generation out of date in some areas. Again, the new Vostros aren’t listed. It still is a more comprehensive list than Lenmar’s.
Obviously, there are a lot of choices here. If you brushed over our feature checklist, you know there is no clear winner. But there are a couple of standouts.
| Brand | Market Price | Cost per Hour of Battery Life (notebook) | Cost per Hour of Battery Life (netbook) |
|---|---|---|---|
| Amstron MedXP 140 | $365 | $98.28 | $43.13 |
| Amstron MedXP 300 | $536 | $51.73 | $26.66 |
| Brunton Sustain | $161 | $57.84 | $31.95 |
| Brunton Impel | $206 | $56.42 | $28.13 |
| Digipower Universal Laptop Battery | $100 | - | - |
| Electrovaya PowerPad 95 | $219 | $62.37 | $36.64 |
| Electrovaya PowerPad 130 | $329 | $62.87 | - |
| Energizer XP8000 | $90 | - | $45.80 |
| Energizer XP18000 | $152 | $56.76 | $31.82 |
| Lenmar PPU916 | $70 | $27.86 | $16.12 |
| PowerTraveller MiniGorilla | $139 | - | $79.11 |
| PowerTraveller PowerGorilla | $280 | $119.50 | $63.44 |
| Tekkeon MP3750 | $110 | $56.65 | $34.52 |
| Tekkeon MP3450 | $117 | $60.26 | $36.72 |
| Tekkeon MP3450i | $155 | - | $49.76 |
Travelers: If you need battery life and frequently find yourself in a situation lacking wall sockets, I would flat out recommend Electrovaya’s PowerPad. These batteries give you gobs of battery life, and if you have a Dell, it’s the only way to go. If you have something other than a Dell, Tekkeon’s MP3750 isn’t a bad choice. Both use an input tip system and allow you to charge your notebook at the same time. This saves close to a pound in luggage, as you only have to carry around one charger. Just toss the battery into your backpack and connect the input tip. When you need power, unspool the output cable. You can keep your notebook’s charger in your backpack, too. When you are at your desk, pull the AC cable out of your backpack and everything charges at the same time.
If you travel internationally, the PowerGorilla is a fair choice because it gives you a decent travel set.
IT Departments: Whether you're talking about a hospital, conference room, or local elementary school, external batteries have been put to use in each one of these environments, and the demand is only increasing.
This time around, our recommendation is split between Amstron and Electrovaya. These are truly industry-grade solutions. If you are trying to minimize the need for cable management, Electrovaya’s input tip system means you only have to deal with one charger. In school, this means one less piece of equipment to purchase and keep track of. That's an important feature if you plan on distributing classroom notebooks on a mobile rack.
For a more business-oriented environment like a conference room, a separate charger offers the benefit of allowing employees to keep the stock charger at their desks. Both brands cost more, but they sell the only batteries in the bunch capable of handling powerful 17.3" and 15.6" DTRs.
Mac: If you are savvy enough to modify you own MagSafe cable (it takes at least a few hours), then we recommend Lenmar’s PPU916 as a cheap and easy way to add more battery life. Whether you are in the air or burning rubber, an external battery is easier to deal with than a power inverter. If you'd rather buy or let MikeGyver modify your MagSafe adapter, I’d recommend grabbing a PowerPad.
Best Buy option: Some features on our checklist may not matter much if you are on a budget. I’d go with the Lenmar PPU916 for anyone feeling a crunch as we near tax day.
If you look at the cost per hour of battery life, it is the only one with a clear lead above the rest. At roughly $28 dollars an hour, the next best consumer alternative is the XP18000 for double the price.
Boaters, backpackers, and those venturing into the great outdoors: I would recommend buying a Brunton. These batteries are more expensive, but they can take punishment. If you plan to be anywhere near water, these are the only batteries that I would feel comfortable recommending. While you can’t go diving with them or hope to recover one from an accidental drop in the ocean, the Sustain and Impel held up very nicely in rain. Brunton is the only one of the roundup willing to honor its warranty, while explicitly claiming its batteries are water-resistant. Add a SolarRoll or Solaris solar panel and you might be able to stay away from the wall socket indefinitely.

Students: If your current notebook isn’t giving you enough battery life, I would recommend either the XP18000 or PPU916. The MP3750 is also a notable mention. Remember that the PPU916 won't charge your notebook. If you are in and out of the classroom, your notebook will thank you for this feature when you get to your last lecture.
Personally, I would lean toward the XP18000. It isn't as small as the PPU916, but it is boxy, so it will stack well alongside your books. Plus, Energizer has a "Free Tips for Life" program. You still have to pay $3.95 for shipping (per order), but you get two free tips per year. If the school is the one issuing notebooks, or if you plan on buying a new system soon, this is a way to ensure compatibility.
Netbook Users: I would tend to avoid the MiniGorilla and XP8000. If you're trying to keep your travel luggage manageable, they aren’t bad choices. But the larger batteries in this story definitely deliver enough battery life to justify a higher price. If you look at the cost per hour of battery life, the MiniGorilla is the most expensive option ($79.11). The XP8000 isn't too far behind at $45.80. You end up paying about 33% less per hour with the XP18000.
Tinkerers: If you are just out to create a really big battery pack, Tekkeon’s MP3750 is the way to go. It is the fastest and cheapest way to create a large battery pack by daisy chaining. The battery furthest away in the chain will drain first, then the second, and so on. If the batteries aren’t capable of dual charging, then you are going to drain from the closest battery in the daisy chain.
I’ll end this roundup with two words of caution. With several of these batteries, it is possible to intentionally select a higher voltage like 24 V and successfully charge a notebook specced for 19 V. This is a bad idea. You are going to put unnecessary stress on the notebook’s power circuits. If you make a mistake and incorrectly select the wrong voltage, that probably won't kill your system. Several of these batteries have overvoltage and reverse flow protection.
The second word of caution is related to warranty concerns. If you buy a Dell battery and it causes damage to your notebook, both the battery and notebook are covered in that first year. According to Dell and Asus, a third-party power solution may void your warranty. Asus told us that, “as long as the third-party adapter is of the correct input/output voltage and power specs, you won't void your warranty.” If the external battery doesn't closely match the power output of the original adapter and damage occurs, then technically the warranty is void. Asus' argument here would be that the damage was caused by not using its stock power adapter. According to Dell, "all Dell-branded power adapters have to pass the Dell qualification process and necessary system-level certification." This applies to external batteries because they function as power adapters. So, if damage occurs as the result of an external battery, your notebook obviously isn't covered.













































