I recently upgraded my MBP to Lion, and now the battery indicator in the menubar at the top of the screen constantly shows "(Charged)", even when the indicator on the side shows almost empty. Any ideas on what's going on or what I can do to fix it?
Edit: It does have an internal battery.
Best Answer
If your MacBook Pro has an internal battery - seek service as they are supposed to self-calibrate and not need any sort of maintenance.
For reference: Apple Portables: Calibrating your computer's battery for best performance
If your model has a removable battery, those are older and the Mac needs you to periodically run a calibration where you charge it to full and leave it connected to power for two or so hours. Then disconnect power and run it down over a day or two - never connecting to power. Eventually, it will go to sleep and then you leave it for 4-5 hours in sleep to finally reach the low voltage shut off.
This will recalibrate the sensor for full and empty and perhaps fix the OS reporting a different charge level than reality. As the battery ages, the "guess" to how much charge capacity is left at a certain voltage level changes. This calibration run should be done every 6 to 10 months if you care to have a more accurate OS battery estimate. Of course, if there is a failure in the battery or the hardware - that will prevent this from working and you will again be seeking service for a repair.
If you are not near a support center - you could try the discharge run on a newer Mac with the newer battery.