Battery dies at 40% power and Mac turns off

Discussion in 'MacBook Pro' started by jbgordon, Jun 14, 2008.

  1. jbgordon macrumors newbie

    Sep 17, 2007
    Hello all,

    I have a problem with my Macbook Pro. I usually keep it plugged in and on occasion use it when I sit on my couch or elsewhere unplugged. Lately, when I have drained the power down to ~40% remaining, my Mac will just shut off as if there is no power left. There is no "low battery power" indication or anything and it doesn't go to sleep, it just turns itself off. Does anybody have experience with this or have any idea what to do? It has happened twice now and I am concerned that there is a problem with the battery because it reaches the 40% level rather quickly...after only about an hour. Thanks.
  2. Heraldic55 macrumors newbie

    Jul 2, 2007
    Something similar has been happening to me. Not only will it shut off at about 40%, the battery life itself has been cut to 1/3 in the past month. I've heard that it is a software problem; that one of the last Leopard updates severely frakked the power management system. Does anyone have a definitive answer on this, and perhaps even a solution?
  3. jbgordon thread starter macrumors newbie

    Sep 17, 2007
    Well, I just spoke to tech support and they think it's the battery. I only have 59 cycles on it and it has only been a year. I don't want to shell out $129 for a new battery already, so I figure I will deal with it and hopefully someone will possibly have a fix for me. I'm running Tiger, not Leopard, by the way.
  4. pianoman181 macrumors regular

    Jan 6, 2004
    That is not typical battery activity. It is not software. The batteries are warrantied against defect like this for one year. If it hasn't exceeded a year or is really close, they may replace it.
  5. jbgordon thread starter macrumors newbie

    Sep 17, 2007
    Tech support told me it was 59 days past the 1-year warranty so I am SOL.
  6. tammy418 macrumors member

    Nov 15, 2006
  7. jbgordon thread starter macrumors newbie

    Sep 17, 2007
    Thanks for the info. I purchased mine in April 07 so I may be able to get a new battery. I'll have to take a trip to an Apple Store.
  8. Kidman13 macrumors regular


    May 16, 2006
    The same thing used to happen to my Macbook at around 10 -15 %. In the beginning I would get a message telling me that I was running on my reserve battery and eventually the Mac would go into sleep mode and save everything to the harddisk. However, after a few months it would just shut down at around 15% battery life.

    I purchased mine around June 2006, and went to an Apple Store around July 2007 with the problem, and even though I was already out of warranty, he just gave me a brand new battery. Now every thing is working perfect.
  9. thomasp macrumors 6502a

    Sep 18, 2004
    I've been getting the same on my 3-year old PowerBook - I just put it down to a worn out battery (approx 200 cycles). Although on an MBP with less than 60 cycles, there's definitely something up

    Strangely, the battery life (according to CoconutBattery and iStat Nano) doesn't change at all, unless the battery suddenly dies like this, where it drops by around 5%. Think I'll live with a "half-working" battery for another year or two, then upgrade the computer!
  10. honeycrisp macrumors regular

    Nov 28, 2007
    Yeah, I've seen this happen on lots of PCs before, but not on a Mac. Must be a really dead battery.
  11. clevin macrumors G3


    Aug 6, 2006
    It shouldn't have anything to do with PC or "Mac", more to do with battery producer.
  12. jbgordon thread starter macrumors newbie

    Sep 17, 2007
    Just got off the phone with tech support again and after showing the woman the info regarding the battery update and that I had purchased mine in April 07, after an hour she agreed to ship me a new battery free of charge. Thanks to all who helped...I appreciate it greatly.
  13. jcroeth macrumors newbie

    Jun 16, 2008
    I see that jbgordon got his problem solved by getting a new battery (congrats), but I thought I would respond anyway because this exact same situation happened to me, and I learned the hard way how not to treat a lithium ion laptop battery.

    Just like jbgordon, I left my laptop plugged in almost constantly. In fact, I only had 17 load cycles after 12 months of owning the laptop, if you can believe that.

    Then one night, during a lightening storm, I decided to unplug my magsafe adapter just to be extra safe and protect against the possibility of a surge (even though I have the adapter plugged into a surge protector). I got down to about 45% and the laptop shut off. It continued to do this any time I got to around 40%.

    I can't remember exactly what my battery health was at the time, but I do remember that it wasn't awful (I think it was above 80% reported in coconutbattery).

    After some online research I learned that my leaving the laptop connected to AC power most of the time caused this problem. It seems that the problem is two-fold from what I understand :

    First, when the battery is not discharged and charged relatively frequently, some of the energy becomes effectively unusable. So you end up with a battery that reports a certain percentage of health, but in fact can only provide a fraction of that percentage of power in real world use. (some of the power gets "locked" in the battery)

    The second problem is that, if you're like me and left it plugged in all the time, you probably never (or rarely) calibrated the battery. The "fuel gauge" on these batteries is actually controlled by a chip in the battery itself, which reports the data to the computer. But if the battery is not calibrated regularly then the gauge will have an inaccurate picture of how much total energy the battery can provide.

    So these two issues combine to create a situation where a battery reports a certain level of health, but can't actually provide that amount of energy (so the battery shuts off before it reports that it's low) and you can't calibrate it to correct the problem because, of course, it's impossible to take it down to zero health. (calibrating the battery by letting it sleep/power-off for 5 hours after it shut off at 40% doesn't work).

    Basically once a battery gets to this level it's ruined. Luckily I was still within my warranty (barely. only by a couple days) so Apple sent me a new battery.

    So the moral of the story is : Don't leave a laptop plugged in all the time.

    jbgordon's battery (or mine) wasn't defective, it was just the constant AC power that killed it. So if you get a new battery, and do the same thing, it will be ruined shortly as well.

    I recommend using the laptop on battery power (taking it down to around 30-40%, then charging it back up) at least twice a month. Apple recommends that you calibrate your battery once every two months, but if you leave it plugged in often, to calibrate it once a month. I do the latter.

    Here is the calibration process :

    EDIT :

    Here are links to the articles where I got most of my information

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