@dihenydd wrote:
On a more cheerful note, a simple NiMH battery pack should be simple to construct to act as a portable power supply. a set of 4 2100mAH cells should provide ~4 full recharges (assuming typically aged batteries and a 500 mA drain - 5 full recharges should be possible in reality). Fresh NiMH x4 would give 5.6V which is above the max for the USB spec (5.25V), but they will sit at 4.8V (USB min is 4.5V) total once they are drained a little until almost flat.
**NOTE:** Let the cells drain before attaching the player (shove them in a torch for a few minutes or something). Also, don’t use alakalies. We can’t assume the players will be happy with >5.25V (although they probably will go somewhat higher
I use a Turbo Charge TC2 (http://www.adrenalinetechnologies.com/products.asp#1) sold for boosting cell phone batteries. It takes 2 AA cells, runs great on NiMHs. I should note that while I’ve referred to the manufacturer’s website, you can find them new for a LOT less if you shop around; I’ve seen them for less than $10 shipped on eBay, for instance. Given all the devices these days that either charge from or can be powered through a USB port, it’s a very handy thing to have - and obviates any problems with voltage matching any sort of cells on their own.
