Are the batteries supposed to die out on you roughly say every 2 weeks ?
Just using generic no-name AA batteries and the keyboards (Microsoft MM wireless rev 1.a ) started dropping letters, generally not responding and even the mouse started to jump a bit.
I use the keyboard quite a bit between say 9-5.30 and the occasional weekend but surely thats not much usage and they should last longer ?
I might try some "branded" batteries to see if that makes a difference.