UberGizmo reports on an Apple Support thread about users finding the batteries Bluetooth keyboards draining quickly since they started using a Magic Mouse. Users have tried using rechargeable batteries and making sure all drivers are up to date, but have been unable to get their keyboard batteries to last for long: they are draining in as little as a week in many reports.
One user put forth the speculation that the Magic Mouse is somehow preventing the keyboard from going into sleep mode, so it keeps transmitting constantly until its battery dies. This is bolstered by a report from another poster, who said that Apple Tech Support told him it's an issue they're working on.
They now claim it is a bluetooth driver issue and the engineers are working on a solution, presumably a new driver or patch. One tech said engineering believes the magic mouse bluetooth is interfering with keyboard bluetooth communication and/or sleep mode. No estimate as to time frame for solution just a suggestion to use rechargeable batteries until issue is resolved.
image via geekologie.com