I had Yosemite working fine on my HP dv6t-7000 laptop, including the battery information in the menu bar using the VoodooBattery kext. Randomly after a reboot, the battery information was no longer displayed. I saw that the box for displaying this information under Energy Saver was unchecked. I then checked it again, but it automatically unchecked itself. This is still the problem. I've tried reinstalling the kext and repairing permissions but that doesn't help.