Jack got a USB cable so he could charge his cell phone from his laptop ($2.50). It appears to work very well. Plug it in the and little battery indicator gives all the signs that it is indeed charging. Wait until it shows that it is fully charged and then unplug it. It will work fine for a bit, but the next day the battery will be dead. Use a regular wall-wart charger and the indicator behaves exactly the same way, but the battery will have enough charge to last for days. So what the devil is going on?
This is the problem with consumer electronics: there is no way to tell. If the charging circuit was a simple, logical one, this kind of thing wouldn't happen. But there could be a capacitor involved, or maybe even a charge-pump circuit, and so the charging indicator is not actually showing what's going on with battery but is instead showing the activity of the charging circuit. And as the wall-wart is delivering 5 Volts, and the USB cable is only delivering 3.3 Volts, all the charge-pump activity in the world won't charge the battery if it doesn't have enough Voltage to start with.
P.S. Google's spell check Fu is weak. It insists that "internet" be capitalized, but it doesn't care about "Volt".
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