|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|
|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|
|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|
|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|
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.