After reading the information on http://batteryuniversity.com, I realize that one of the best ways to permanently damage a lithium ion battery is to use the battery at a high temperature while it's fully charged. This is exactly what happens when you use the computer as if it were a desktop computer, since leaving it plugged in will keep the battery at 100% and using the computer will heat up the battery. This is why it's recommend to remove the battery from your laptop if you are using it is this scenario.

My question is what would you do if the laptop doesn't have removable batteries (e.g. a MacBook Pro)?

Should I use some kind of charge cycle such as: charge to 80%, unplug the power chord, use the laptop until it reaches 20%, then repeat the cycle by charging to 80% again?

If so, which values should I use instead of 80% and 20%? (I think charging to 80% is better than 100% because of the damage that a hot battery at 100% can do, but I just made the figure 80% up, and I'm sure there's a better number to strive for which is backed by science.)

I've read many of the articles on batteryuniversity.com, but couldn't find anything pertaining to this.

Update: What about doing something like charge (or discharge) it to 50%, then plug it in and turn on settings which use the battery as much as possible (e.g. brightness all the way up, wi-fi on, etc.), in order to try to maintain the battery at 50% (i.e. the rate it is charging is the same as it is discharging). This will probably heat up the battery, but would make it so you don't need to constantly plug and unplug the laptop. The one bad thing is that you are taking up more charge cycles which would decrease the battery life, thus I'm not sure this is a good idea.

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    The Sony Vaio laptop has software with it that does just that - limits the battery charge to 80% so you seem to be thinking on the right lines. – BrianA Dec 19 '10 at 18:50
  • @BrianA: do you know at what percentage the Vaio starts charging again? – Senseful Dec 29 '10 at 16:02
  • I'd love to see a piece of software that will smart-charge a Macbook Pro like you mentioned for the Sony – th3dude Dec 29 '10 at 16:05
  • no sorry. It always seems to sit at 80% with the power supply plugged in. Unplug it and the battery discharges. Plug it in again and it goes back up to 80%. Only annoyance really is remembering to 100% charge it if you want maximum time on battery. To do that you have to change the set-up. I rarely need that so leave it in battery saver as default. – BrianA Dec 29 '10 at 18:39
  • Note that modern battery management systems make this issue and advice obsolete. – David Schwartz Aug 4 '17 at 18:53

Usually it would be good to keep the battery between 80-ish and 20-ish percent full, it would extend the battery life, but how long will it be extended? The battery is virtually guaranteed to lose its capacity after two years. Probably a more realistic (or pessimistic, depending on how you see it) is to grab an AppleCare package then when the battery loses its charge significantly they can replace it for you.

  • It seems that AppleCare doesn't cover the batteries: " b. Limitations. The Plan does not cover: [...] (ix) Consumable parts, such as batteries, except in respect of battery coverage under APP for iPod or unless failure has occurred due to a defect in materials and workmanship;" – Senseful Dec 29 '10 at 17:15
  • @Senseful Darn. Nonetheless, a macbook battery costs $200 to replace. – digitxp Dec 29 '10 at 17:26

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