This was not something expected by owners of a Magic Mouse with the Wireless Keyboard, but it can be a really worrisome problem in the absence of some efficient fix by Apple.
It is not known for sure what happens, but according to some users of the Wireless Keyboard, since they use the Magic Mouse the keyboard battery disappears very quickly, something that did not happen before.
Without a doubt a fact that Apple has to investigate and try to solve, since it is not logical for something like this to happen.
Source | applesphere
True, I have noticed that since I acquired the wireless keyboard, the batteries drain at a disastrous rate, they do not last more than a week. I've tried looking for solutions like firmware update and can't find a way to make them last longer. I hope apple does something about it, I'm going to leave the pay in batteries !! and this has happened since I bought the magic mouse! I've thought about changing it, but it works so well with my mac mini that it wouldn't be the same. Greetings and I love your website !!
I bought an Imac 21,5 ″ in November 2009 and observed the same thing (the keyboard batteries lasted about ten days. What I do now is turn off the keyboard every time I turn off the Imac (by pressing the button for more than two seconds until turn off the pilot) and turn on the magic mouse and keyboard at the same time, before turning the Imac back on. Today (5/01/2010) the keyboard is at 87% and the mouse at 73% after about 70 days ( 3 hours of work a day on average) In case the advice is worth it, but they spend a lot of battery ... we will see if in Cupertino they will put the idem ... Happy 2010 to all the maquer @ s.