| If you really need to run that thing for a month off one charge, why | not go all the way with a couple of LiPo cells?
I'm not sure LiPo is such a good idea.
1) two cells will put out 6.0 to 8.4 volts. If the device takes only
5-6 volts, you'll need a voltage regulator. (I wouldn't worry about the heat -- it can't use too much power.)
2) The mp3 player probably doesn't know to stop discharging at 6 volts. So he could happily run down the LiPo cells too far and ruin them.
3) There is the danger of incorrect charging. Fires and explosions are unlikely, but they do happen.
4) You won't be able to use a cheap charger with it -- it'll need some smarts. Failure to use the correct charger will ruin the cells at best, and burn everything down at worst.
| You can get quick chargers and they have to match the type of cells | you want to use. Check at those same RC Stores.
If 4 AA NiMH cells will physically fit (what kind of batteries does it take stock?) then I'd go with that. Especially if it's what it was designed to use.
As for a charger, I wouldn't bother with a peak charger if this is all you need it for. A 100 mA receiver pack R/C charger would work fine, and it would charge it fully in about 2000 mAh / 100 mA * 1.20 or about 24 hours. Just make two battery packs and charge one while you use the other.
Don't leave your battery packs on this charger 24/7 -- it wears the batteries out. Take them off the charger once charged. NiMH cells discharge at about 3%/day, so after a month or two they'll be dead if not charged.
If there's a R/C swap meet around where you live, I'll bet you could get a R/C charger for under $5 -- no need to pay big bucks for it.
You could also use almost any wal-wart transformer and an appropriate resistor, but that would require some math and measurements and such.
| > Also, does it matter if I get a NiMH or NiCad charger, or are RC trickle | > chargers compatible with both types of battery?
Yes, the slow chargers will work with both. But the extra capacity means that charging takes that much longer.
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