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I'm using MacBook Pro and it will be in charge nearly 12 hours in a day. I set the battery indicator to Percentage, so it is displaying the battery charge in percentage.

The problem I faced is, most of the time it showing 100%, but in some times, it stops (I don't know exactly) charging in 97% or in 99%. For a long time, it remains same until I discharge the battery then put again in charge.

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What is the problem here?

Am I using the battery in the right way?

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1 Answer

up vote 2 down vote accepted

This is by design. It's not helpful to fully charge a battery, and then use a little bit (say 2 or 3%) and then top it back up again. So purposefully, if you have fully charged your battery, it will not start to recharge it until such time as it has lost sufficient charge for a recharge to be worthwhile. It's all about charging your battery efficiently, resulting in minimal wear and tear where possible.

So, to try to illustrate it by example:

  • You start with a flat battery, and charge it. It gets to 100%
  • You move desks or something, resulting in a few minutes of battery usage, dropping it to 98%, then put it back on power
  • The system decides it's not worth topping up 2% worth, and just sits there. The green light probably shows on the Magsafe to indicate that it's not even trying to charge, likewise the menubar icon shows a plug indicating full charge, rather than the lightning bolt charging indicator
  • You use some more battery, say dropping it to 92%, before putting it back on charge. The system now decides that 8% is worth bothering about, and starts to charge.
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Great!! Thank you :) –  Confused May 17 '12 at 14:16
1  
Out of interest, the iOS devices do much the same thing, but they do it a lot more gracefully. 100% isn't actually full on iOS, it's just what it says is full, they will actually continue charging to (say, for example) 106%, and when they hit that they will use battery for 6% until they drop to 100%, then charge again etc - all for the sake of battery efficiency, it's better to use them than leave them, and if you do leave them, fully charged is not the best idea (about half is considered best), so this way allows continued battery use to prevent failures and degradation. –  stuffe May 17 '12 at 14:23
    
+1. Great answer! –  macaco May 17 '12 at 14:47
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