Check out something called a precharged rechargeable battery. Sanyo Eneloop is a good one. Unlike other rechargeables, the hybrid type don't have the high internal discharge so they stay charged when not in use. Sanyo's only come in AA and AAA sizes and you need to use spacers with AAs for C and D cell applications. A Google of Sanyo Eneloop will turn up lots of places to buy them and reviews from users.