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How to reset your laptop's power management unit System
Recently, someone on a mailing list had terrible trouble with his iBook batteries draining very quickly (empty after 1 hour, 45 minutes max). He noticed the hard disk didn't spin down. Suspecting it was the OS X energy saver somehow not working, he searched days for a fix, but didn't find anything. System updates came and went, but still the problem persisted. Until finally someone dug up the following Apple Knowledge Base article:

PowerBook and iBook: Resetting Power Management Unit

I know it is perhaps not really OSX related, but I've seen other people struggling with this bug, thinking it is OSX related, so I figured I could only help by spreading the word.
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How to reset your laptop's power management unit | 11 comments | Create New Account
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Authored by: megasad on Nov 15, '02 11:27:22AM

Since 10.2 I've been getting 1 hour maximum out my one year old iBook, where in 10.1 I'd get 2 1/2 to 3 hours. So I'm on my way home now to try this out and if it works I shall be a happy bunny...

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Authored by: megasad on Nov 15, '02 03:47:01PM

Alas, I am a sad bunny. I did what was said, but my battery still only lasts 1 hour. Oh well.

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Authored by: wuf810 on Nov 15, '02 05:18:31PM

Drop the brightness of your screen down a few notches - it makes all the difference.

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Drat (maybe not!)
Authored by: BTPearcy on Nov 16, '02 10:01:31AM
I had the same problem, and much to my surprise, Apple considered my battery covered under Applecare! Sent the computer in (it also had a broken latch) and back it came with a brand spankin' new battery, and now I get ~5 hours on my iBook (with the screen down to the lowest brightness setting of course). So if you are still covered, send it in!

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Authored by: Marco Cottone on Nov 19, '02 05:57:54AM

If there is a process that read/writes data at regular intervals of time, the hard disk never spins down. Maybe an investigation about this could help?

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Mac OSX and Power Management
Authored by: hschickel on Nov 15, '02 11:50:52AM

If you're having power management type problems it would also be helpful to delete the following:


If you look in /var/db/SystemConfiguration you'll find a number of interesting settings that can become corrupt. If you're having problems with Networking, airport, power management, or if you clone one machine to a different model of machine it's a good idea to trash this whole folder.


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Follow UP
Authored by: hschickel on Nov 15, '02 11:53:09AM

I forgot to mention - when mucking with the above folder it's best to be in single user mode.


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Same Issue
Authored by: Platkus on Nov 15, '02 07:54:55PM

I am having this same issue with my 1 year old dual USB iBook. After upgrading to 10.2 the battery life is almost half of what it used to be. No settings were changed. The thing that I think is causing it is that the hard drive does not spin down during normal usage of the computer like it used to. This constant spinning would account for the decreased battery life.

I've reset the power manager, but that did not help. I will try deleting the power management file listed a few posts up to see if that helps.

Any other recommendations would be greatly appreciated.



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some power management tips
Authored by: dnordwall on Nov 15, '02 11:13:59PM

In jaguar, they took away the fine control over power management there was in 10.1. Fortunately, editing of the file above can help.

Remember, that disk has to spin up every time it needs to do _anything_ on the disk. Website sets a cookie? yep. Asks to set a cookie and you deny? yes, because, depending on your browser, it will record the fact to disk that you are denying that site! web page caching, yep. Try turning off web page caching and denying all cookies. Of course, at that point, a lot of web sites (including this one) will not work the way you expect.

Another one I've caught myself on is logging of iChat. I like to keep the logs, but those write to disk as well, and cause spin up. Your mail client will as well, as it caches local messages. If you can stomach it, and have the ability, use ssh and get your mail remotely, using pine.

My hard drive spun down just a second ago, which is a fair chunk faster that it normally does. I set my spin down time to 2 (minutes) in the file mentioned above. Nice work

If you can possibly manage it, and your hyper about power management, hook up a usb keychain drive and put your home directory on that. Those use much much less power. Not only that, but I wager it would provide some system security. Then again, my iTunes folder is bigger than the biggest usb keychain drive by a couple times.

Overall, I'm fairly disappointed with the battery life on my older powerbook g4. I expected much better, but I'm seeing around 2 hours regularly. I have coworkers with new dells that can shove in 2 batteries and pull 10 hours out of it

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some power management tips
Authored by: serres on Nov 17, '02 03:04:54AM

pmset - modify power management settings

since 10.1.4 (?) we have a command line utility called "pmset", see

% man pmset

with it you can modify the relevant power manager related settings available in mac os x (i looked at the source intensively). it even has some commented out stuff for future use like the "wake from sleep at some date" setting we had in mac os 9. for some non-understandable reason these are not implemented in the mac os x power manager library :(

you should also use this utility to modifiy the PowerManagement.xml file.

i think what's *very* important to save battery power is to enable the "Reduce Processor speed" setting.

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HELP - lost date + time preference pane
Authored by: cyberRodent on Jan 21, '03 03:18:26AM

Hi -
I Have a Lombard powerbook running os 10.2.3 that was failing to wake from sleep about 50% of the time - I read the article on apple's site and shutdown and pushed the reset button - I expected the date and time to be reset -- it wasn't, only the time zone was changed but now my date and time preference pane is GONE! Does anyone know any way that I can regenerate this? would if work if I copied the preference pane file from another machine and replaced my now 0k file that way? any help will be appreciated - Hopefully I can resolve this before its time to change the clocks in the Spring!!! -- xo Jeff

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