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NormPhillips · Oct 1, 2006, 04:36 PM

Hi. I usually have my MacBook Pro 15.4" 2.16GHz laptop attached to the power outlet (I almost never use the battery as the chief power supply). When my battery is charged, the battery status menu item indicates I have 100% power. However, every so often it indicates 99% instead of 100%. To correct this, I temporarily disconnect the laptop from the power outlet and then recharge it back to 100%.

Is it normal for my MacBook Pro's battery to be doing this?

Thanks.

JKT · Oct 1, 2006, 05:35 PM

Once the battery has fully charged, it isn't actually charging anymore even though it is still plugged in. After reaching 100%, the battery will slowly lose charge until it drops to below 95%, at which point it will recharge once more. This is done to increase the lifespan of your battery as multiple very small charges (which is what would happen as it isn't physically possible for a battery to stay at 100% even when plugged in) would otherwise shorten it very quickly.

pcummins · Oct 2, 2006, 09:47 AM

Also the functions that calculate the battery percentage round down. Most of the time the battery will lose 1 or more points over time (usually an hour) and drop to 99% (when they mean 99.95% or thereabouts). I wouldn't worry about it, but if you want the real readout you can get programs to give you the capacity (usually 4400, or around there... varies per laptop battery type). You'll see that it's nothing to worry about.

Eriamjh · Oct 2, 2006, 04:05 PM

JKT is right.

Once the battery reaches 100%, it is "bad" to try to hold it at 100%. So the power supply goes into a PWM mode. That means it charges and stops, charges and stops. It keeps the battery from overheating. To reduce the current down to a mere trickle to prevent the charge-loss, would require a more expensive charging circuit and you wouldn't want to pay for it.

quattrokid73 · Oct 2, 2006, 04:37 PM

Is it better to continually cycle the battery or keep it plugged in for desk use but make sure it gets cycled once every few days?

I generally have my macbook pro on the desk, so its near the charging cord, but i want to do wahtever is best for it.

adam

JKT · Oct 2, 2006, 06:24 PM

Apple recommends discharging fully once a month (for Li-ion batteries, I don't know about Li-polymer) if you use it primarily as a desktop - they even offer an iCal calendar alarm to remind you - I've always taken that to mean do it all in one go if you like.

Frugle · Oct 2, 2006, 09:19 PM

then what are cycles? when looking at iStat, my MBP is at 97% and 86 cycles. what does that mean?

quattrokid73 · Oct 2, 2006, 09:30 PM

hm well i think once a month seems quite sparing. with the lipo and lion batteries i use for my rc helis, it's good to discharge them more than that as long as the discharge/recharge rate is healthy.

adam

JKT · Oct 3, 2006, 03:32 AM

Originally Posted by Frugle

then what are cycles? when looking at iStat, my MBP is at 97% and 86 cycles. what does that mean?

Each time your battery loses the equivalent of a full charge (and that can occur in multiple stages), it will have gone through a cycle. E.g. if you discharge 25%, recharge to 80%, discharge 25%, recharge to 100%, discharge 50%, you will have put your battery through one discharge cycle (25%+25%+50%). Your battery should last for a few hundred cycles before it starts to go kaput (if you treat it well).