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Using two batteries: powerbook gets confused

Message #1 - Posted 2006/07/29 - Markus Dehmann

I have a Powerbook G4 with two batteries. Once the first battery runs out I put the other one in and vice versa.

But Mac OS gets confused about the life times and doesn't save its state anymore before shutting down. The problem is that one battery life is shorter than the other. So at some point Mac OS assumes I have the longer battery in, but I am really running on the shorter one. So Mac OS isn't prepared when the battery runs out. It doesn't save state and I lose the Spotlight index, the clock is reset to Dec 1, 1969, I think, and I lose other data.

What can I do? There must be other people using two batteries on a powerbook?

Thanks!
Markus

Message #2 - Posted 2006/07/30 - David Empson

Markus Dehmann wrote:

I have a Powerbook G4 with two batteries. Once the first battery runs out I put the other one in and vice versa.

But Mac OS gets confused about the life times and doesn't save its state anymore before shutting down.

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.)

David Empson
dempson@actrix.gen.nz

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