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The following is an extract from System Information (under power):

 Charge Information:
  Charge Remaining (mAh):   6517
  Fully Charged:    Yes
  Charging: No
  Full Charge Capacity (mAh):   6690

Is this simply an example of the charger not topping up the battery to conserve cycles, poorly calibrated battery or an issue with my machine's battery?

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up vote 3 down vote accepted

"Fully charged" does not mean exactly 100%, but somewhere between 95% (or even less) and 100%. Obviously it is better for battery life if the battery is not immediately loaded after a small percentage of charge was consumed, if your MacBook is connected to the charger. So you do not have an issue with your battery.

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This took me a while to get used to as well but it really is normal behavior for Macs. –  Zrb0529 Sep 1 '12 at 5:03
    
Thanks for your response! Last night I experimented by running my machine on battery down to about 80% and then recharging it while it switched off - ended up with the same numbers for both. This morning however I switch on my machine and notice that 'Charge Remaining' has reduced slightly despite being plugged in all the time. Also I noticed that the Full Charge Capacity has also reduced slightly i.e. to 6685. Is this normal? –  jpoh Sep 2 '12 at 2:17
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The Full Charge Capacity decreases with the lifetime and number of cycles of the battery. So now and then you will see a slight decrease. If you want to follow and write down the development over time, you can use a tool like Coconut Battery. –  vilmoskörte Sep 2 '12 at 5:42
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