battery capacity question

Discussion in 'MacBook' started by deraj090, Feb 25, 2010.

  1. deraj090 macrumors regular

    Feb 18, 2010
    I just bought my macbook this past weekend. I've noticed a drop of over 100 mAH in my battery's full capacity, after two cycles. Is this normal? Does this drop slow down?
  2. miles01110 macrumors Core


    Jul 24, 2006
    The Ivory Tower (I'm not coming down)
  3. deraj090 thread starter macrumors regular

    Feb 18, 2010
    thanks for the simple "normal" answer -- i appreciate that haha. that link you provided doesn't really tell me much, though...
  4. Pax macrumors 6502a

    Dec 12, 2003
    I think that's OK.
    The actual capacity is just a guess.
    The battery charging circuit doesn't know exactly how many mAh are in the battery. It can only keep track of how many mAh are taken out and put in. By doing this it estimates how many mAh are in the battery at any time. But this estimate gets less accurate with time. That's why calibration is useful once in a while. Calibration just means charging the battery right up to 100%, running it down to 0%, and counting how many mAh come out. Also when it charges right up again it can compare mAh with voltage to learn what the max capacity is.

    It's like a bank account where you can never see the balance, just money going in and out. Over time your estimate of the balance might get less and less accurate. The only way to find out what the balance really is, is to go to the ATM and keep taking money out until it stops letting you!

    Over time you will see the estimate of max capacity wander about a bit. If it differs a lot from 5100 mAh or whatever the start point is, it's time to calibrate.

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