Ok, so I have an iMac with a Magic Mouse and all the latest software installed.
I just got the apple rechargeable batteries. They have been in my MM for about two weeks. After the end of the first week, my battery life on the MM was down to 75% according to the iMac.
Today when I come into work, my same batteries are estimated to have a battery level of 100%.
How can that be? What crazyness !!! (I suppose this could have something to do with my installation of the new Mac OS update yesterday, but not sure how....)