I have a Pixel 8a, which is certified qi1, and 2 devices that can wirelessly charge it, a baseus battery pack and an ESR phone holder, they're both certified qi2 (which is backwards compatible with qi1), yet when I charge with them I can at most reach ~2.2W charging instead of the 7.5W advertised maximum for my Pixel 8a.
I don't understand why that is and if I can even theoretically reach the maximum supported charging power.
If so, how would I test my devices to figure out what their real thresholds are or if there are incompatibilities somewhere?