All digi camera eat batteries. What I was told is that you need to buy the highest mh rating you can find.

Jessops have these 2000mh with a charger for £13

Sony 2300 for a score

As for camera anything 3MP upwards is fine for most ordinary use. (goes up to 10x6" IIRC.

And if you get a separate card/media reader which runs on USB then you wont need to have the camera on to put the pics on your computer. Which is good for battery life.

Personally Id spend a bit more than £100. Nikon 4MP £140
Canon 3.2MP £160