Wow! 3 months for any cordless mouse is good!!! Mine used to die in like 2 weeks, but I'm a heavy gamer

Anyways, keyboard is going to depend on usage, but still much much better than the mouse b/c there's no LED to power.
I'm using the cordless keyboard from my Cordless Freedom Optical set along with the MX700. Batteries aren't an issue b/c of the charger, but I have to change the keyboard battery once very 3 or 4 months (4 AA, newer Elite models only use 2 AA and supposedly last just as long). If you use rechargeables, expect to replace them more often.
Chiz