wireless keyboard eats batteries

I have a MBP running OSX 10.7.5, and my apple wireless keyboard has suddenly (as of a couple of weeks ago) started eating batteries. 5-8 hours, I will go from 100% to 12%. Prior to this, over the last year and a half, its been fine, I would maybe change batteries about once a month, if that.

I am not using a magic mouse with it, its a wired mouse.

I tried flashing the PRAM once.

Can anyone help?