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Mobility Check: Battery Life

Is On-The-Go Storage Ready for Primetime?
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The N1050 carrying sleeve even has room for the battery pack.

Both devices ship with a battery pack, to enable mobile use. Each of these battery packs holds 4 AA batteries. In choosing batteries for these applications, we strongly recommend rechargeable nickel-metal hydride (NiMH) or nickel-zinc (NiZn) batteries - otherwise, you will have to buy lots of disposable batteries. Even when using alkaline batteries with nominal voltage of 1.5V, which makes six volts available versus 4.8V from rechargeables, it's still advisable to use rechargeable batteries with a 1.2V rating whenever possible. This seemingly contradictory advice reflects the way that the voltage available from one-time use batteries falls with use, and results in average delivery of 1.2 V over the battery's lifetime. In addition, alkaline batteries may even deliver less than 1.0 Volts under load, whereas NiMH rechargeables deliver a nearly constant 1.2 V during the entire load period.

Once voltages dip below a certain threshold, the drive motor will not run correctly any more; when this happens, the device emits a clattering noise. This can occur even when the batteries retain sufficient reserves to deliver current. It probably would have made more sense to house six cells in these battery packs, and to include a voltage regulator as well.

When NiMH rechargeables with a rated capacity of 2000 mAh are used with a drive that consumes 0.5 A of current, this produces a theoretical battery life of four hours. Because the actual current draw varies from drive to drive, and the devices that are attached to an OTG device also draw some current, however modest, the real-world battery life varies between 30 minutes and three-and-a-half hours.

When it comes to data transfer to an external drive, it's the controller in the external enclosure that's the bottleneck rather than the disk drive itself. Because of this, the hard disk that you choose to install in the drive enclosure is not as important as the controller when it comes to maximizing performance. Also, neither a fast drive nor a fast controller will do anything to boost throughput if a USB 1.1 connection is used between the OTG device and a card reader. This explains why the data transfer rates for various attached devices can vary so widely from one to the other. It's also obvious that it doesn't really matter if you use an UltraATA or a SATA drive in an external drive enclosure, as our test results show.

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