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Macbook battery stange behaviour
Lodbrok
Registered User regular
Registered User regular
So, I've had my macbook for about a year. During this time I've tried to not use the battery to much in order to not degrade it more than necessary. Now, i know these batteries lose capacity both from use and from increasing age, but I still felt it was a good idea to work with computer plugged in when I could. Today I noticed something strange. If you use istat nano, you can look at the battery section and see a number indicating the health of your battery, reported by the circuits in the battery itself I presume. Up until today, the health hovered around 96%, but today it was suddenly down to 62%, and when running on battery power, sure enough the computer reported something like 2 hours of run time from a full battery. Now when I look again, it is back up to 77%.... what do these numbers actually mean, and what is happening to my battery?
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Also, if you go to the Apple menu->About this Mac->More info->Under hardware choose power, over on the right will be some battery information. What's the full charge capacity and cycle count?
You might be able to get the battery replaced by Apple if the run time is too low but I'd run through this fairly general checklist before calling them up since they'll just get you to do it all anyway:
1. Re-calibrate the battery. http://docs.info.apple.com/article.html?artnum=86284
2. Reset your SMC - http://docs.info.apple.com/article.html?artnum=303319
3. Reset your PRAM - http://docs.info.apple.com/article.html?artnum=2238
4. Insure all software is up to date, ESPECIALLY insure the 1.2 battery update is installed - http://www.apple.com/support/downloads/batteryupdate12.html
If all else fails, call em up explain you did all that stuff and have the full charge capacity and cycle count ready if they ask for it.
Oh, here's the Apple site regarding MacBook and MacBook Pro battery issues:
http://www.apple.com/support/macbook_macbookpro/batteryupdate/
The health percentage is just the current capacity divided by the original capacity (rated in milliamp-hours). But the battery is guessing at its current capacity based on the last time it was able to watch the power disperse from full-to-empty. It's like you guessing the current capacity of your car's fuel tank by filling it up and then driving it until the car stalls, and then filling it up again and looking at the number on the fuel pump. The battery has to do the same thing (metaphorically speaking).
Try "calibrating" the battery (run it from completely full to completely dead).
The advice to reset your PRAM is something that used to be more relevant to Mac OS 9 (which stored a few more things in that region than OSX does). Still, PRAM doesn't store (and never has stored) anything related to the battery.
"What's stored in PRAM?" [apple.com]
Besides which, if you do reset your SMC, it will reset the NVRAM anyway (to include PRAM).
There are a few practices in Mac troubleshooting cultures that are like voodoo. Reset your PRAM, repair your file permissions, etc. I feel like they continue to get suggested far too often, but they're basically just superstitious habits at this point.
Ya, after posting it I thought about it and realized it's probably a pointless step as I was thinking of a different power related issue article that has the step listed. Also I forgot that it's the Mac Pro that the PRAM doesn't get cleared out when you do the SMC reset.
Go to the Mac store and they should just replace it for you. Happened to me a few months ago