do yourself a favor...
Your battery use seems high, however the mouse does seem to chew through batteries at a quick rate, especially when compared to the keyboards. Buy yourself a set of Sanyo Eneloops, or the new Apple branded rechargeables (which are probably Eneloops anyway). Amazon usually has the best pricing, and Costco carries them too. While there was some kvetching about the Apple pricing it isn't really off the mark.
The batteries are awesome, they do NOT discharge when they are not being used, like most batteries and especially the rechargeables. I have an extra set so I always have a fresh pair ready.
If I am working constantly I can have to replace the batteries in as little as 10 days, although a month is about average. Keyboard lasts about 3 times longer...
cheers,
michael