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Comment by tjoff | Hacker News Reader

You are right but I disagree.

Yes, devices do not charge batteries to 100% as that is directly damaging. And they don't discharge to 0% for the same reason.

So they charge to something slightly less. But that slightly less is for all intents and purposes the only definition of 100% we, as end users, have.

It's like saying that your CPU is actually only running at 70% clock frequency but overclocking it to 100% would require massive cooling and reduce the lifetime to months.

I agree a better definition and preferably one directly comparable to all brands and battery types were available, but I'm not aware of any and I'm sure that even if we had it you wouldn't trivially be able to get that information.

Noone should ever charge to more than 80%. That is short sighted and environmentally moronic. After less than two years a device will have more capacity at 80% than the same battery will have at 100% if it was charged to 100%.

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While I agree with your general take and hate that my iphone can't be capped to 80% [0], and love that my otherwise crappy hp laptop can be capped to something like 85% (and reports both cap and max capacity), I don't agree with your final take.

To take the phone example, mine usually ends the day around 85%. I just don't use it too often. But I sometimes absolutely do and would trade months of battery life for not being left without battery in the middle of nowhere. And the 20% can make all the difference.

A few years ago, I rented a car in a foreign country on a foreign continent. It didn't come with a USB port, and I didn't have a cigar adaptor. When I arrived at my destination, at night, my phone's battery was 10%. I sure as hell am happy that it was charged to a "full" 100% instead of dying on me one hour earlier.

Sure, I could have grabbed an external battery or something. Not sure how much environmentally smarter that is, since it would basically rot away in a drawer somewhere, since I would basically never use it.

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[0] Where does this 80% come from? Would it be even better if I stopped charging at 60%? I rarely use more than 20% of my phone's battery, so that would be largely enough, but I sometimes absolutely do and would hate to have to lug around external batteries "just in case".

Of course. All we're asking for is an optional "limit charge to 80%" feature. And, just like macOS has, you can have a very easily accessible "charge to full now" option for those times when you know you're going to need a full charge.

Don't forget, "100%" isn't really 100% any more after a year or two of charging to 100% all the time. You've probably lost 20% or so of your battery's capacity and it will be charging slower due to increased internal resistance.

> "Where does this 80% come from? Would it be even better if I stopped charging at 60%?"

Yes, but only marginally better since there's diminishing returns. 80% is generally considered to be the sweet spot that best balances practicality with battery health.

> just like macOS has

Can you please direct me to where this is possible in MacOS? I can't see any option to configure a charging cap except some "smart" option which has been on this whole time but always charges to 100%.

It's not possible to set a hard limit in macOS without third party utility like AlDente [1].

I was referring to the built-in "Optimised battery charging" feature. When this is active and has decided it will cap charging at 80% [2], you get a "charge to full now" option in the battery menu.

[1] https://apphousekitchen.com

[2] I do agree that this feature sucks and rarely actually works, unless you have a very predictable charging schedule.

I leave my laptop plugged in 95% of the time so in practice this caps it at 80% (helpful).

I suspect quite a few people do that so it probably is net-good overall, but agree it doesn’t work well if you’re moving around a lot.

Absolutely agree.

But my response was to the parent comment (emphasis mine):

> Noone should ever charge to more than 80%. That is short sighted and environmentally moronic. After less than two years a device will have more capacity at 80% than the same battery will have at 100% if it was charged to 100%.

My point is that I find there are legitimate uses cases for sometimes charging to 100%. And, indeed, those cases are much better served if most of the time I only charge less. In my case, this could be much less (50% of my iphone's battery is more than enough 360 days a year – and I know beforehand when it's going to be one of those 5 remaining days)

But that 20% that makes all the difference will only make a difference when the phone is new.

Otherwise the opposite is true. Refraining to charge fully makes all the difference and saves you from a tough spot.

Which in turn is why (was a bigger problem before) the sentiment that it doesn't matter how good/bad battery life I have as long as it lasts me a day. Well, if you do a complete cycle every day a year old phone will not last a day anymore...

This used to be an easy problem to fix, by replacing the battery.

Shame that seems to be harder and harder to find on new phones.

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