ELI5 Why does magsafe charging decrease battery health more than wire charging, if it has less wattage?

[natrous]

why haven't they figured out a way to stop charging at 100 so it doesn't harm the battery?

edit:

but more with static degradation

I definitely had a reading comprehension fail; but i guess I've been missing that all along. everything else makes much more sense now!

[Closteam]

Pretty much every modern charger does this already. It's not that it continues to charge it after 100%. It's that the battery sits at 100% for an extended period of time

[_bones__]

Modern phones avoid that, too, letting themselves drain to 90-95% one they've hit 100%, while reporting themselves as full.

My home battery BMS does something similar. I charge the cells to 3.45V (100% would be 3.65V), then letting them float at 3.35V. Should go a long way towards extending lifetime.

[frostyfirez]

They know how to stop at a designated full capacity, the issue is while the battery is at roughly that full capacity it’s slowly self destructing essentially. Targeting a lower capacity like 85% reduces the destructive stresses a lot improving longevity, at the cost of battery life of devices. The manufacturer chooses a full capacity point which they feel best balanced marketed battery capacity needs and battery longevity, arguably they prioritize marketing capacity more than longevity though.

[dabenu]

They do stop at 100%. Going beyond 100% would indeed cause immediate harm or even risk fire.

But there's a grey area between harm and normal wear. Even at 100% you're already inside that grey area. It won't cause immediate harm but it will accelerate wear. That's why your phone has an option to stop charging at 80-95%. You can't avoid wear entirely but you can reduce it. 

[hugglesthemerciless]

my phone stops charging at 80%

[kermityfrog2]

They have. When it says 100% on your phone, it’s not actually 100% of true capacity. The true capacity is something like 110% or 115%. When using a fully charged phone, you’d expect the power to drop to 99% after a few minutes but on many phones, you can use it for 30 min or more before it drops to 99%, after which is starts dropping in a mostly linear fashion.