this post was submitted on 29 Jan 2024
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How, tho? Sounds like what we had for e.g. NiCd batteries (memory effect) but do not have for li-{ion,poly} ones.
Also, why would the laptop discharge the battery with ac attached? Sounds weird to me
Lithium-ion batteries these days do not have a memory effect, but will degrade when kept at 100% charge because the internal composition of chemicals will change, destroying the battery in the process. The ideal charge is between 20% and 80%. With (better) battery charge control you can extend the design capacity (the maximum charge the battery can hold when new) and lifespan. With AC attached, the battery will discharge but it will be charged when the minimum charge level is reached.
Huh, apparently some vendors kinda do it themselves (not sure if always, tho) at least for the lower bound:
cat /sys/class/power_supply/BAT1/voltage_min_designreports 10.8v for a 3s battery which is about 3.6v per cell instead of 3.2. Also the upper limit is uncertain so farI don't really understand that argument, and I want someone to correct me:
If you were keeping your battery at the ideal charge (i.e. 20% to 80%) that means you are really only using 60% of your battery during its lifetime. I've been using my phone since July of 2021, always changing it to 100%, preferably only charging when it gets close to 0%. Using AccuBattery I get the battery stats and after 2 years and a half, the battery capacity is at 85%.
I still have 85% of usable battery, this is more than the 60% I'd get if I was using the battery ideally. So I don't really get this argument about taking care of the battery cause it appears it would take a while before the battery is degraded enough to hold less charge than the recommended rate.
There's other things that happen to a battery as it ages. Voltage sag with heavy current draw is one. An app that measures capacity may not take this into account. It may look fine and be at full voltage with light usage, but then launch a CPU-heavy app and it drops down a few tenths of a volt and isn't able to hold the voltage.
If it's discharged enough, sometimes this will drop the voltage enough to cause the phone to shut off even if it has a decent charge, say 20-30%.
You'll notice this in reverse too. The battery will seem to start charging faster than usual, but then the rate drops off dramatically as it gets close to full.
As a drone enthusiast, I'm pretty familiar with this effect because we abuse the shit out of our batteries.
85% after 2.5 years is not good. My car battery has guarante of 80% capacity after 6 years. 20% of range is a significant difference so I take car of my battery and don't charge it above 80% if not needed. It's the same with laptops. Current models can easily last 5-10 years but having only 50% of capacity after that time would be a problem. Sure, if you're intending to throw it out after 3 years it doesn't really matter but if you want to use it for as long as possible you definitely should take care of the battery. It's pretty much the only part that degrades (except maybe keyboard).
Stopping charge at 80% (and still going down near 0%) should give you roughly 4x the cycle life. So in theory doing that it would take about 8 years to hit the same 85% usable level.
85% left after 2.5 years is a high rate of wear, due to phones really pushing as much as they can into the battery to have longer run times.