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I just discovered (from an Android app called AccuBattery) that fully charging a lithium ion battery is significantly harder on it than charging it to only 80% or less. Most of my devices use lithium ion batteries, and most of the time (especially Windows laptops) I leave them plugged in because I'm at home or at work where power is readily available. I'm wondering if this is hard on them, and, if so, why utilities have not arisen to limit the charge to around 50% when the user knows they're not planning to need battery power for a long time. Is maintaining a 100% charge all the time damaging? Is there a balance regarding the frequency at which charging from 50% to 100% and using the battery back down to 50% breaks even with maintaining 100% charge and using it down to 50% at the same frequency?

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For modern laptops, this usually isn't much of an issue unless you're regularly connecting to and disconnecting from AC power. Most modern laptops have power distribution systems that work very similarly to an uninterruptible power supply. When connected to AC, they will run off of that and keep the battery topped up, but they will switch to battery power if disconnected from AC. As a result, if you're plugged in all the time, you aren't cycling the charge on your battery, you're just running on AC power (and usually applying just enough charging current to the battery to keep it from losing charge by itself). In addition, a couple of OEM's actually do provide support for this type of thing (provided you install their bloatware on your system and you're using WIndows). Dell has has this for years on their systems for example.

There are however a couple of issues with not charging the battery all the way:

  1. Users won't consistently get the battery life they expect. As a very specific example, I almost always use my laptop plugged in, but on the occasions I do need to use the battery, I almost always need a full charge (I've also got a behemoth of a mobile workstation though, so full charge is about 2.5 hours if I'm lucky).
  2. Cheap batteries can actually develop reduced capacities faster if not charged all the way.
  3. Adding more logic to the embedded controller for the battery (which is part of what would need to change, because that's what handles charging on almost all systems) to handle this opens up new opportunities for bugs in an area that you can't afford to have bugs.
  • I don't understand how partially charging a battery can result in reduced capacity and fully charging a battery can also result in reduced capacity. What's a person to do? My Nexus 6P battery capacity is down to 25% of its original capacity, possibly because I kept it fully charged most of the time (though there may have been other hardware issues with this phone) so I'm trying to better understand battery maintenance in general so I know what to do after I get it back from warranty service replacing the battery. – BlueMonkMN Aug 30 '17 at 12:46
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    The issue is regularly partially charging a battery. Rechargeable batteries wear out eventually regardless (think about any times you've had to replace your car battery for example), it's just a matter of how and when. Some are designed to be kept charged at full capacity most of the time (like car batteries, because you need a significant discharge to start the car), others are designed to gracefully handle regular partial charges (like a lot of phone batteries). There's really no way to know as a consumer though which is the case for a particular battery. – Austin Hemmelgarn Aug 30 '17 at 12:59
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    To give slightly more concrete advice for your particular case, charge your phone when it needs to be charged, don't just leave it on the charger all the time. Most phones are designed to run throughout the day and be charged overnight. – Austin Hemmelgarn Aug 30 '17 at 13:00
  • For what it's worth, the manufacturer, Huawei, gave me similar advice after repairing the device (Nexus 6P had issues anyway) and replacing the battery. They went a step farther and suggested plugging it in in the early morning so as not to ever leave it plugged in while fully charged. – BlueMonkMN Sep 21 '17 at 23:30

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