Mac Forum / General / Portable Macs / July 2006

The battery lifetime information is stored in nonvolatile memory in the
battery, so it is surprising if the computer is "forgetting" it.

It might just be that one or both of the batteries needs to be
recalibrated. Fully charge the battery, then unplug the power and use
the computer until it goes to sleep by itself due to low battery level,
then plug the power in again until the battery is fully charged. This
should store correct calibration data in the battery.

Another issue is that swapping the batteries without the power supply
connected relies on an internal device which holds a small amount of
charge while there is no power source. If this device is faulty then as
soon as you pull out the first battery the computer will be powered
down. When I first got my PowerBook G4 (Titanium) I could swap batteries
with the computer asleep and not lose anything, even with no battery
connected for something like ten to thirty seconds, but three years
later it didn't work like that any more (or maybe it just needs to be
done faster). I don't have two batteries handy so I can't check it again
now.

Note that some Apple laptops don't have this feature, so you cannot swap
batteries without the power supply connected. Check your manual to be
sure.

(My understanding is that in general, PowerBooks do support this
feature, with the exception of the 12" models. In general, iBooks don't
support this feature. Don't know about the Intel models: I would expect
it to apply to the MacBook Pro but not the MacBook.)