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A chemist told me that a battery should be charged to and used between 30-70%, and its very bad for battery life to completely load or unload it.

He uses a utility program that always keeps the charge of his Lenovo laptop between 30% and 70%.

How can I achieve the same effect using Mac OS X?

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Why care about battery life degrading (let's say to 80% of original levels, which is a significant discharge) when that's still more energy than keeping it deliberately only at 70%? –  Daniel Beck Aug 18 '12 at 10:09
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If you care about your battery life, the most important thing to take into account is temperature. High temperatures (>35C) will permanently damage a batteries capacity. Low temperatures have a similar temporary effect. Also, modern batteries need to be used for maximum performance. If you don’t use your device often or have it hooked up to a power source all the time, be sure to complete a charge cycle at least once a month. See here for more info. I wouldn't worry too much about the whole 30-70% thing - couldn't find any evidence to support that claim –  Thomas Ploeger Aug 18 '12 at 10:32
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@ThomasPloeger The claim you couldn't find any evidence for is mentioned in the Wikipedia article about lithium ion batteries. –  Daniel Beck Aug 18 '12 at 11:50
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@ThomasPloeger Good question. I still see this as a problem of long-term storage though, especially since the computer's heat will advance battery deterioration independent of load level. We seem to have several good questions about the general topic in the battery-life tag. –  Daniel Beck Aug 18 '12 at 12:57
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@DanielBeck The reasoning is essentially that we would prefer, on extended desk-bound sessions, to keep the charge constantly at, say, 60%, which is in the long run less detrimental than keeping it constantly at 100%, all else being equal (a power adapter ready and willing to supply juice). Just before a trip or any normal portable usage session, the battery is to be topped off to 100%. I do believe that for most of us, myself included, the benefit of always being at the ready with battery fully charged outweighs that benefit. I think it's legit to want a way to keep a specified charge level. –  Steven Lu May 30 at 17:50

3 Answers 3

Based on this article:

  • Use partial-discharge cycles
  • Avoid charging to 100% capacity: why don't you unplug the charger now and then? Or try that software : http://fruitjuiceapp.com/ (Note: I haven't tried it myself...)
  • Limit the battery temperature: make sure your laptop is well vented, and do not forget your laptop in your car during the summer.
  • Do not charge your battery in a cold environment (<0deg Celcius). The charger circuitry is supposed to monitor the temperature but just in case...
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A little addition regarding useful softwares (OK they do not prevent from charging above a certain level, but they may help): coconutBattery, very lightweight, and MiniBatteryLogger, that logs your battery history. This one is a little bit old but works on my 2012 Macbook air. –  sdive Jan 16 '13 at 8:21

I didn't find a pure Software solution, so I've set up a quick hack based on the Belkin WeMo Switch and a Node.js app. The WeMo is a power outlet that can be switched on and off via Wifi. So you can plug your laptop charger on the WeMo, and a script or an app running on your laptop monitor the battery and switch the outlet on and off accordingly. You can find an example of source code on my blog

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That's awesome! I wish I could get all my li-ion powered devices to do that... –  Protector one Aug 21 at 18:22

I really don't think this is an issue.

A full charge by itself does not significantly reduce the lifespan of the battery, unless it is stored at full charge for more than about two weeks. Your primary concern should be heat and unnecessarily deep discharges (to 20% or lower state of charge). Heat is the predominant concern with laptop batteries, because lithium-ion batteries degrade significantly faster at high temperatures that at low temperatures.

If your laptop allows it, detach the battery when it is fully charged while running on the AC adapter, so that it is not subject to the heat generated by the computer. Optimal battery life can be obtained by limiting the depth of discharge to about 50-60%, or discharging the battery to not less than 40-50% state of charge after a full charge. Detailed technical information on how to extend the life of lithium-ion batteries can be found in this Battery University lesson.

This is how I've maintained as much as 80% of the original charge capacity of my laptop's battery after 2-1/2 years of use.

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