View Full Version : Does anyone's battery, while plugged in, still says 100%?

Feb 7, 2009, 08:48 PM
When i don't need to be portable, i keep my MB connected to the MagSafe Power Adapter. I just noticed that its at 99%, for the last hr....

just curious, will i ever get it back to 100%, or is that the natural life of the battery?

Feb 7, 2009, 09:23 PM
This is perfectly normal, to save the battery , it wont start charging until it hit (i think) below 95%, so if you unplugg it at 99% charge, it won't start charging again.! :cool:

don't worry its fine ! :D

Feb 8, 2009, 03:09 PM
My MBP 2.2Ghz with a brand new battery does this too, sometimes it will stay at 96%, 97%, 98%, 99%, 100% (sometimes)

it does fluctuate when plugged in from 96-100% so im not sure if its releasiing electrons to keep it fuller and better capacity or if im actually losing charges/cycles whiles it splugged in and its going down like that.

but either way i believe it should be fine

Feb 9, 2009, 09:53 AM
It's actually a function of preserving battery life. Lithium ion/polymer batteries are not like many of the other rechargable battery technologies of the past. For one, they do run the chance of exploding or catching fire, but that's not usually a concern for most people.

Here are some basic rules about lithium ion batteries that will help explain this and some other issues that people have.

1. Lithium ion batteries start to degrade pretty much immediatey from the factory. So fresh batteries will always hold more charge than older batteries just by age. (My alu macbook I just got which has a build date of 10/08 has lower watt/hr rating on it's battery than the alu macbook I got with a build date of 12/08 and returned) So always buy the freshest batteries, and expect they will degrade regardless of how well you baby it. (with some caveats below)

2. There are some things about the battery chemistry to know.

A. Lithium Ion batteries do not like being at 100% charge all the time. The batteries are actually happiest at about 40% charge. Full charges actually make the battery lifespan shorter. This is totally impractical from a use perspective, I know. But if you have a battery that you will be storing or not using for a while (month etc) having it partially discharged will make it lose less battery life.

B. Lithium Ion batteries do not like deep discharges, and can be damaged by them. ie the battery calibration procedure. If you drain your battery down to very low levels it can damage the battery itself and really shorten the lifespan. Which is why it's not recommended to do the battery calibration procedure frequently. Also letting the battery die through regular usage and not charging it before then will do the same thing. (Some people wonder why their battery life gets worse even though they frequently calibrate it, this is why)

So the long answer to your question about the 96-100% is that apple is smart enough to not keep topping off the battery to 100% thus shortening it's battery life, theoretically the battery would last longer if they picked a lower point to start recharging, but that would cause alot of consumer headaches and be less practical.

So if you want to prolong battery life, deep discharge down to very low levels as infrequently as you can. Don't be overzealous with the discharge/battery calibration. If you want to store the battery, do it in a cool dark place @40-50% charge.