Seems that the battery readout percentage is a little flakey on the imac. I bought the imac 3 weeks ago, and the keyboard readout still shows 100%. However, the mouse was down to 43%. I turned off the mouse earlier today, and then turned in back on. After several hours of use, the level is now at 80%. These are not rechargeable batteries, but the original batteries. I could see the level resetting to 100% after replacing batteries, but turning the mouse off and on should not cause it to go from 43% to 80%.