MacBook unibody Polycarbonate battery problem

Discussion in 'MacBook' started by himanshupant, Apr 17, 2010.

  1. himanshupant macrumors newbie

    Apr 17, 2010
    First of all thanks for this splendid forum and the insights we get on Mac on this...

    I had been a life long Windows user ( close to 15 yrs) when I shifted to Mac this January. I purchased a white unibody polycarbonate macbook. To admit , I immediately fell in love with the machine , the speed , the smoothness really got to me..But of late I am having worries over my battery

    Till one week back my battery charge cycle count was 25 with battery health as 100 % .. I was using the macbook in a pretty normal way i.e. keeping it in AC mains most of the time and discharging it some time upto 70 - 80 %. I went for caliberation as per the instructions given in apple support site and to my dismay after the caliberation the battery health fell to 94 % and now its to 91 % with charge count as 27... Is something wrong with my macbook or the battery ?

    I am posting the snapshot of the charge information.

    Charge Information:
    Charge remaining (mAh): 4938
    Fully charged: Yes
    Charging: No
    Full charge capacity (mAh): 4963
    Health Information:
    Cycle count: 27
    Condition: Normal
    Battery Installed: Yes
    Amperage (mA): -153
    Voltage (mV): 12464

    To start with the FCC used to be close to 5400mAh and now its down to 4963 :( . This way I am worried that the 300 cycles and 80 % battery health might come way too fast... Please help me in understanding this erratic behaviour of battery.... I am using iStatPro to check up the battery health along system profiler

    Furthermore the default warranty is for 1 yr which I guess means that if the battery FCC drops to less than 80 % before 300 cycles in 1 yr then Apple would replace the battery free of cost.. If I take apple extended care for 3 yrs then will this battery coverage extend to 3 yrs ??
  2. Pax macrumors 6502a

    Dec 12, 2003
    Panic not. There are loads of threads about this on here.
    Well done for posting your battery info.

    The problem the Mac has is that it doesn't really know the full charge capacity of the battery. It has to guess. The Mac just charges the battery until it reaches 12600 mV. And it counts the amount of charge that goes in and out as you use it. Over time this accounting gets out of whack and its FCC estimate gets less accurate. Calibration is basically emptying the battery and filling it right up again, counting the charge that goes in. Then the Mac has a good idea of the FCC.

    The problem is, the FCC depends on lots of factors:- the temperature; what your Mac is doing while it charges; age of the battery etc etc etc. So a calibration will only give you an FCC figure which is accurate at the exact time you charged the battery. If you calibrate the battery on two consecutive days you will probably get two different FCC values.

    Analogy:- your car has a gas tank whose size varies in an unpredictable way. Sometimes it holds 9 gallons, sometimes 10. When you fill it til the needle says "full", how much gas is in the tank? Answer - you don't really know. The only way to tell for sure is to empty it right out and fill it again, keeping an eye on the gas pump readout. But even then you only know its capacity on that day. Tomorrow its capacity might be different.

    So the 91% figure is just a guess. If you calibrate it tomorrow you'll get another, probably higher, figure. Search these forums. You'll see loads of people who post that their FCC number wanders about. Mine varies from about 90% to above 100% (yes, above). Ignore your FCC for a month. Then look again. I bet it's >91%.
  3. ulbador macrumors 68000


    Feb 11, 2010
    Call up Apple. At the point your battery is at, they will replace it. I just got mine replaced at a nearby Apple Store after a call to Apple Care and mine was in better shape than yours.

    I bought my MacBook on February 11th. The battery had 22 cycles on it and was floating between 89 and 93%, which was about an average of 5050 mAh. I took it in there, they booted it up with an iPod nano into a Battery testing program, and within 20 minutes they had installed a new battery. While my battery was still in "the green zone" portion of their application, it was far lower than it should have been after 22 cycles and two months.

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