Adaptive Charging on Pixel devices gets most of the way there: it will learn how long it's typically on the charger each day, and automatically slow the rate of charge to match, so that it finishes approximately an hour before you usually unplug it.
There's a manual option to turn it off (charge at full rate this time only), but not to manually turn it on (such as giving it a target time to be fully charged). Older Pixels used what time the alarm was set as the target time to finish charging, which I preferred as someone who doesn't wake up at the same time every day; I'm not sure why they took that away.
The adaptive charging used to be great for me, and then I had a baby. Now I get up a few times in the night, and so the adaptive charging just defaults to full rate. My night is still going to "end" at the same time so slow charging is fine, but my phone doesn't know that. I wish I had an override.
(I do have an old, lower wattage charger beside my bed to limit the charge rate)
Another problem is the constant charging and discharging of battery while connected to external power. I believe the latest pixels got or will soon get the ability to run directly off the wall when connected to certain chargers.
I would love to see this technology come to all phones. 80% cap might be controversial but I don't think what I am asking for is controversial in the least.
> Another problem is the constant charging and discharging of battery while connected to external power.
Is that actually the case? Anecdotally, all my devices which spend 99% of their time connected to external power show the least degradation in reported capacity and the best preservation of their original battery life. I'm talking about iPhones, macbooks and hp laptops.
For the latter, I have two basically identical ones, one for work and the other for home (same model number, same generation, same battery p/n). The home one rarely if ever runs on battery, it has something like 50 cycles in 4 years. The battery lasts pretty much as when it was new. The other runs often on battery and it only lasts half as much. I doubt it's a lemon, because it's the standard issue laptop at work, and my colleagues' are in the same boat.
My iphone 14 pro's reported battery health has also degraded much faster than my iphone 7's. I use it much more often on battery than the old one which spent 90% of its time plugged in. But since the devices are different, the comparison isn't as meaningful as with the laptops.
Some devices will notice when they've been plugged in for a very long time, and will automatically discharge the battery to 80% or so, but continue to report 100% state of charge to the user.
Chemically speaking, Li batteries do degrade much faster when kept at 100% for weeks on end compared to being stored at 50%, but not as fast as cycling it. The absolute worst case (without cycling) is being stored at 100% at warmer temperatures, like 40C. They will lose over 10% within a month in those conditions. I highly suggest a laptop cooler for any desk where you may use a laptop plugged in for extended periods.
That's... really not how this works. As a person designing lithium management circuits, you typically have a very small delta-V for top-off charging. We're talking ~0.1V. Once full, the charge circuit disconnects. If the battery is under load or self-discharges below your dV, charging starts back up usually at a very low current. Top-off is also totally optional, it's just a common feature.
Additionally, only the cheapest of cheap garbage phones would behave the way you imply. Charge controllers are readily available from TI et al with battery bypass. When the battery is full, the system runs on external power exclusively, except for the top-off charge.
It's really a pretty standard feature. You can get controllers with and without this, but you'd have to be either extremely cheap or extremely dumb to not use a controller with battery bypass in an application like a phone.
Based on my own testing, my pixel 8 will run on USB. No current fluctuations that would indicate battery cycling, just a constant draw. My previous Samsung also behaves this way.
You're right that cycling the battery this way is bad for them, that's why competent engineers don't.
I found this source about pixel phones and bypass charging. I also know anecdotally that leaving phones plugged in with screen on, I have gotten spicy pillows more than once. I would love to learn how to avoid this spicy pillow problem.
There's a manual option to turn it off (charge at full rate this time only), but not to manually turn it on (such as giving it a target time to be fully charged). Older Pixels used what time the alarm was set as the target time to finish charging, which I preferred as someone who doesn't wake up at the same time every day; I'm not sure why they took that away.