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Comment by rb808 | Hacker News Reader

Its amazing how dumb most charging is for smart devices. I plug my phone in every night and it does a quick charge then sits there and does nothing the rest of the night. It even knows my alarm clock time, surely it should be smart enough to slowly charge all night.

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iPhones will selectively delay charging past 80% if you're at home and if your usage history indicates that the phone will be left on the charger for a while longer.

https://support.apple.com/en-us/HT210512

Apparently a notification will show up when optimised charging is enabled. I’ve never seen it, because the functionality also requires Significant Locations and other location services (listed near the bottom of the page) to be enabled.

That seems to me to be quite unfriendly to privacy. And given that I always charge my phone overnight and use my phone’s alarm function, it could simply use that as the target time to finish charging to 100%. No complicated location-based ML needed.

It’s all on device so I don’t think there are any significant privacy implications.

My Asus Zenfone 6 just looks at my next alarm for this purpose.

At least, it would be nice if they told me about this requirement on the Settings sheet where I enable "Optimized Battery Charging". I was wondering why it never seems to kick in. Thank you for the clue!

Having the machine know your location has nothing to do with privacy issues.

Having the machine upload or make available that information to someone else does. I don't know what the Mac does here.

It's not necessarily that it's dumb, there's a bit of battery physics and chemistry involved. If you look up EV charging curves for example [1], the first bit goes fast and the last bit slows down. A rough analogy I've heard is it's like blowing up a balloon -- as it gets bigger, there's more back-pressure so it gets harder to fill up the last bit. That's why the EV roadtrip strategy is "frequent fast-charging" -- you spend less time if you recharge from 10% to 60% twice instead of going from 10% to 100% once (also safer to take driver breaks).

If your phone never gets past 80%, it could be the battery just needs replacement. Batteries are consumables, and they do degrade after a year or two or three (depending on cycling, temperatures, use, etc). iOS has a battery health indicator giving you a rough estimate of the state... if the health is low, get a repair kit from ifixit and then it's a fun evening activity to open one of those puppies up and see just how tiny everything in there is!

[1] https://www.google.com/search?q=ev+charging+curves

This is a total tangent but I can't resist:

"it's like blowing up a balloon -- as it gets bigger, there's more back-pressure so it gets harder to fill up the last bit."

That's not actually the case with a balloon. :)

If you think about it I'm sure you've noticed that you have to blow the hardest right when you start, and then it gets easier. The reason has to do with the curvature of the balloon and the fact that the same amount of air causes less and less stretching of the material as it fills up.

It's not that adding additional charge to the battery is difficult. It's that the current has to be tapered off when the battery is near-full so it doesn't go over its rated voltage.

Thanks for the clarification, the analogy clearly isn't very good.

Out of curiosity, have you found a better ELI5 analogy that doesn't bend over backwards with a rube goldberg setup of pipes and waterflow? I've struggled explaining this phenomenon to people buying EV's, where charging behavior become a regular thing people need to figure out.

Well, if they're familiar with beer, and sophisticated enough to pour it into a glass: poured very quickly, the beer will develop a large head that overflows the glass, but pouring slowly creates a smaller head (or none, but don't do that).

There's not more beer, but it fills more space temporarily when poured faster.

That's not a bad example, I'm gonna try it out. Thanks!

They aren't saying that the charging circuit is dumb because it slows down as it gets nearer to 100%. (That's how it works when it is trying to charge as fast as it reasonably can.)

Instead, they are saying it's dumb because it doesn't slow down when it can charge fast but doesn't need to charge fast.

If your phone is at 40% and you plug it in, it will probably finish charging in about 2 hours. But if you plug it in at bedtime, you don't need it to be done in 2 hours because you'll still be asleep. So why not figure out the lack of urgency, then take 4 or 5 hours and keep the battery temperature lower?

On my old Galaxy Nexus running CyanogenMod, quick charging had to be explicitly activated. I still think that off-by-default is the most sane configuration, as I've rarely needed it.

> it should be smart enough to slowly charge all night

I have a Sony which does this (XZ1c, stock firmware)

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