Just don't get confused by the tech detail about voltages... external USB PSUs are 5V devices as are USB computer ports... this is what USB provides and this is what you are supposed to supply to the reader... getting to specific voltages, for the actual battery, is handled internally...
Quote:
Originally Posted by Pinecone
Actually it uses a lithium polymer battery.
The are rated at a nominal 3.7 volts, but like all rechargeable batteries, there is range of operating voltage from fully charged down to the maximum safe discharge. For Lipoloy (or Lipo), fully charged is 4.2 volts and fuly discharged in 3.0 volts.
So to fully charge, you need a source of at least 4.2 volts.
The way that lipos are charged is a constant current - constant voltage curve. They start with a constant current (for long life a maximum of 1 x capacity, so for a 940 mAH battery, 940 mA charge rate). Once the charger voltage reaches the fully charged voltage (4.2 volts) the charger holds this voltage until full charged. Since the charge current goes down as the battery gets fully charged, you really can't overcharge them, unless you put in too high of a voltage.
Also, a lipo life is limited by the number of charge cycles, but it is based on full charge cycles (3.0 - 4.2 volts). If you only run it down 1/2 way and charge, it only counts as 1/2 cycle. So no problem with charging when the reader is not fully discharged.
Also, as I understand it, the light goes out at 80% charge, it take another hour for it to fully charge. Although, it is hard to mark 80% and very easy to mark 90% charged. 90% charged is when the charge voltage hits the max voltage (4.2 volts).
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