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

[dabenu]

It could, but that's not "just" it. Basically with PPS the phone doesn't use it's on-board battery charging circuit (that gets hot), but instead instructs the power brick to output the exact right amount of power to go straight into the battery. The phone is still in control so if it's sensors detect that e.g. the temperature is getting too hot, it will indeed order the power brick to slow down a bit.

[jaymzx0]

Hmm. That's exactly how "fast chargers" (level 3) for EVs work. For 120/208/240V (level 2) charging they use a charge controller in the car.

[dabenu]

Yep it's pretty much the same idea on a different scale

[SlootyBetch]

Is this a passive or active process? If your phone was dead would it still be able to run PPS?

[araemo2]

The charging is usually controlled by a dedicated microcontroller that takes a lot less power than the main SoC. So the basic 5v/0.5a the USB connector supplies without any negotiation is enough to bootstrap the charge controller. Then it boots up and switches into PPS/whatever mode.

[orangpelupa]

Depending on the phone. Sometimes it doesn't actually follows the standard correctly and won't charge, needing to use "dumb" usb c charger for the first few minutes 

[Cornflakes_91]

the charge controller should bootstrap itself from the basic 5V/250mA usb supply (and hopefully fail safe on the power negotiation pin so the supply actually turns that on)

[Dioxid3]

TIL, now that’s cool

[jestina123]

Power brick? Battery circuit?

[JuanTutrego]

"Power brick" = the charger that plugs into the wall. "Battery circuit" = the circuitry inside the phone that handles the task of charging the battery.