I think the main battery is the only battery on these, they don't have a backup battery. The Service Source manual is not a lot of help, it just shows you how to do upgrade the Ram and AirPort under the keyboard, which is also documented in the standard user manual - it looks like they never wanted anyone to open these up. The service manual says to reset the power manager you use the little reset switch above the power switch where you have to stick a paperclip or something in.