4x 1.2 rechargeables will be fine for about 2 charges (Get 2300mAh types if you can). I even heard there are 1.25v ones available so if you can get those which will = 5v. Using 6v is probably a bad idea. Might fry it with prolonged use.
Shame you can't use standard alkalines as that would be useful if you are stuck with no place to charge from. Still at least this is something. I got a battery pack from Maplin on the cheap (Like £3!) that works great
