TL;DR
- Android 15 is preparing to tweak the threshold that determines whether a charger is seen as fast, from a measly 7.5W to a more reasonable 20W.
- The operating system has long considered any charging speeds of at least 7.5W to be fast, which is far, far below what actual fast chargers can deliver nowadays.
- The change isn’t live yet in the latest Android 15 beta, though, so chargers that deliver 7.5W of power will still be seen as fast on Pixels.
I’ve only ever seen it when running a game or when a chromebook got plugged into a 5w charger, so I’m guessing it’s when the OS does the math and decides it can’t rev down enough to make headway while booted up.
It’s also possible to have voltage issues on a device with multi-cell batteries.
My laptop charges on a type-C charger, but only if it can get 15+ volts. If it’s a 12V charger, that isn’t enough to push a charge into its battery. It will run on 12V but won’t charge at all, even if it’s off.