I have had my iMac since June and changed the batteries last month. Now I am getting another message saying the battery life is low in my mouse. I replaced the original batteries with two basic Energizer batteries (I have not had a chance to get rechargeable batteries for future use). I am a fairly heavy computer user 4-6 hours per day. Is this relatively normal battery life and is there any thing I can do to extend the battery life? Should I close the laser door on the bottom of the mouse when I go to sleep/am not using my computer?