I'm thinking about getting a wireless keyboard and mouse and am wondering how often new batteries must be put in. I know that it probably varies with different setups, but if I could get a general idea that would be great.
thanks.

My wireless Logitech mouse needs batteries changed about every 3-4 months...though, sometimes i change them it needs the sensors cleanned...

Some mouses like the Kensington ones come with a little dock-like charger. When you are not using it you just stick it into the charger and when you use it you take it out. Simple, no worries about replacing the battery.

My wireless (optical) mouse needs new batteries every 1.5-2 months, and the keyboard even less frequently.