13 Replies Latest reply: May 28, 2009 3:51 AM by ct44
Chuck Smith 2 Level 2 Level 2 (190 points)
I think I already know the answer but I want a confirmation:
My battery has 388 charge cycles and fails always, around 30-40 percent, without a warning, ever. The green lights on the battery indicate their should be a charge but even then i cant start it back up without the power chord... i tried to reset it but can follow the insrections since I never get a wrning and it never drains completely.

Is it time for a new battery?

MacBook Pro, Mac OS X (10.4.11), 2.4 Ghz Core2 duo, 2 gigs RAM
  • dwb Level 7 Level 7 (21,725 points)
    Your battery is certainly well used but the early death (in percentages) probably is caused by an uncalibrated battery. As you use the battery, over time, its onboard chip and the computer get out of sync and the computer isn't able to estimate battery life properly. Apple recommends that you calibrate your battery about once a month:

    To calibrate the battery:
    1. Plug in the MagSafe power adapter and fully charge the MacBook or MacBook Pro battery until the light on the MagSafe connector changes to green and the Battery icon in the menu bar indicates that the battery is fully charged.
    2. Allow the battery to rest in the fully charged state for two hours or longer. You may use your computer during this time as long as the power adapter is plugged in.
    3. Disconnect the power adapter with the computer on and start using it with battery power. When the battery's charge gets low, you’ll see the low battery warning dialog on the screen.
    4. Continue to keep your computer turned on until it goes to sleep. Save your work and close all applications when the battery's charge gets low and before the computer goes to sleep.
    5. Turn off the computer or allow it to sleep for five hours or longer.
    6. Reconnect the power adapter and leave it connected until the battery is fully charged. You may use your computer during this time.

    After you've done this your computer should give you a warning rather than simply shutting down with no power and your time/percentage estimate should be accurate. I've found that after calibrating the accuracy will improve over the next couple of days. So, after you've done this you can look at your full power time estimate (and usage) and decide if its time to replace the battery.
  • Chuck Smith 2 Level 2 Level 2 (190 points)
    I have to say though, the battery use time varies from 20 mintes to the full 3 hours...
    I never get a dialog, thats the problem... it just shuts down... when I leave it off and come back to it, my computer still tells me that it's 30% full... even though i've done the steps exactly as said...
  • neuroanatomist Level 7 Level 7 (31,690 points)
    The procedure dwb described is a battery calibration - something you should do every couple of months. If you have never done one of those, the battery eventually loses the ability to be calibrated, and the only solution is a new battery. Coupled with your cycle count approaching 400 (the useful lifespan of a typical Li-based battery is 400-500 cycles), I'd say it's time for a new battery.
  • dwb Level 7 Level 7 (21,725 points)
    The lack of a shut down warning and that you shut down with the battery showing it has lots of power left are both clear signs of an uncalibrated battery which is why I recommended you do it. Of course the number of cycles your battery has is a concern too, and it may be time for replacement but I've gone over 450 cycles and still gotten acceptable battery time on some batteries and barely 300 with others.

    I've also seen cases where a badly out of calibration battery benefitted from a second calibration run a few days later. And not to be insulting but I also know that lots of people don't quite follow the instructions and wind up merely discharging and recharging the battery which isn't a calibration.
  • Graham K. Rogers Level 5 Level 5 (5,430 points)
    Neuroanatomist, and/or Chuck: I don't think I am threadjacking as I have the same battery dies after random periods of time problem, and that may well be due to a lack of calibration over some time. Would you happen to know (approximately) what the replacement cost is?

    They are rather expensive here (around $320) and I will be in CA early next month, so could buy one then. I had searched the online store (US) and could find nothing.
  • neuroanatomist Level 7 Level 7 (31,690 points)
    US$129, plus 8-10% sales tax in CA (depending on where in CA).
  • Graham K. Rogers Level 5 Level 5 (5,430 points)
    Magic. That is going to save me a bundle. SF, by the way. Thanks Neuroanatomist.
  • Chuck Smith 2 Level 2 Level 2 (190 points)

    Mu batery officially cracked and leaked... got a replacement from applecare...
  • ct44 Level 1 Level 1 (0 points)
    I have the problem of computer shutting down at approx 40% battery also. But how can I follow the procedure you describe if the low battery warning dialog does not appear?
  • ct44 Level 1 Level 1 (0 points)
    I suppose what I am asking is how can I follow the battery calibration procedure if I cannot let the battery run down until it sleeps. It shuts down at approx 40%. So I am wondering how I can do the calibration. My battery has only done 191 cycles. Sorry for butting in on the thread but I have similar woes.

  • dwb Level 7 Level 7 (21,725 points)
    Don't worry about it automatically going to sleep - when you get near the 40% save your work and then keep using the computer until it sleeps. During calibration you are supposed to use the battery until the computer goes to sleep so that's not a problem.
  • ct44 Level 1 Level 1 (0 points)
    But it does not go to sleep - it shuts down totally and requires a restart with the power
  • dwb Level 7 Level 7 (21,725 points)
    Go ahead and follow the instructions as is. Let it turn off and then follow the resting instructions. Afterwards I think you'll see the estimated time is more accurate. Sometimes a battery that is badly out of calibration benefits from a second attempt but use the computer for about a week first and do your best to avoid using the power converter until the battery is close to being discharged during that first week.