Battery Charging and 80%/40% Rule


Well-known member
May 28, 2011
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I've read several times about ideally charging your batter once its gets no lower than 40% up to 80%, so that is stays generally healthy. With the technology in chargers now, where they wont damage your battery if you leave it plugged in, is it now ok to charge the battery up to near 100% and let it roll for the day? I know the 80% rule generally keeps it healthy because it doesnt cause a "full charge" to be registered but is this really still necessary today to keep your battery in good shape?

thanks in advance.



Super Moderator
Feb 6, 2017
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There been some different options about this over the years , 40/80 from 3rd party sources say it's best , the phone manufacturers been quiet on this , so I very been doing 5% to 100 for long time with really no issues and occasional overjoyed charges. I have my iPhone 10 still original battery down to 83% capacity and iPhone 11pro 98% my Samsung I haven't kept long enough to know lately but have my pixel 4xl still running great. It's you what works best I don't think you can go wrong either way.


Feb 23, 2011
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The charger itself only becomes a concern when it comes to the rate of charge relative to battery capacity. That is something tightly controlled by spec and the charging protocol of the phone, so not much of a problem for us.

The 40/80 rule (or perhaps guideline is a better term) has to do with the state of charge. Li-ion batteries become more susceptible to degradation at very low and very high charge levels, regardless of the charging method. In other words, if you set 3 identical Li-ion batteries on a shelf and unplugged, with the only difference being one fully charged, one at 15%, and one at 50%, the 50% charged battery will degrade slower than the other two.

Something else to keep in mind is heat. Heat alone can also degrade a battery, but heat plus a high charge can degrade it exponentially faster. If the phone feels warm to the touch, or you are actively using it, then it's more important to unplug early. The lower the charge level, the less heat will degrade the battery, but going too low is still problematic.

From personal experience, I once killed a battery in about 6 months by keeping it fully charged at all times because I thought I was saving cycle counts. I've had my current LG V60 for just over a year while strictly following the 40/80 rule, and have no degradation according to AccuBattery.

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