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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 g

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

lutorm 6y ago
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.
Zak 6y ago
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.
- floatrock 6y ago
  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.
  - Zak 6y ago
    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.
    - floatrock 6y ago
      That's not a bad example, I'm gonna try it out. Thanks!
adrianmonk 6y ago
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?

lutorm 6y ago

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.

Zak 6y ago

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.

floatrock 6y ago
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.
- Zak 6y ago
  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.
  - floatrock 6y ago
    That's not a bad example, I'm gonna try it out. Thanks!

adrianmonk 6y ago

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?