Painfully, painfully obvious. But a good place to start. Buy rechargeable batteries for obvious reasons. Nickel Metal Hydride (NiMH) are better than rechargeable alkaline batteries. NiMHs can be charged thousands of times before they need to be disposed of or recycled (try Call2Recycle which has thousands of drop-off locations in the U.S. and Canada). If you are not going to recharge, then buy alkaline batteries. They maintain their power longer than NiMH batteries. NiMH's are terrible if you don't plan on recharging them.