Qi wireless charger can discharge iphone - really?

[P_Watt]

Got a cheap Qi certified (apparently) wireless charger with lovely LED lights round the edge.
This particular charger will charge to 100% then shut off.
As far as I knew charging is a one-way process so I was surprised to see this battery graph which is repeatable.
If I remove the phone from the charger at 100% it will retain its charge, but if I leave it on there to “trickle” charge it will discharge at an alarming rate instead. Surely the opposite of what may be expected.
I’m happy to return or ditch the charger but I don’t understand how this can happen.
Graphs show left on and taken off the charger after 100% charged.
iphone 12 ios 17.3 beta 3

 

[ManuCH]

Could it maybe be that the phone tries to keep connecting to the charger after it's at 100%, the "handshake" somehow fails, and therefore it uses a lot of power trying to do that the whole time? Seems to be an incompatibility between that specific charger and the iPhone.

 

[P_Watt]

Could it maybe be that the phone tries to keep connecting to the charger after it's at 100%, the "handshake" somehow fails, and therefore it uses a lot of power trying to do that the whole time? Seems to be an incompatibility between that specific charger and the iPhone.

That makes sense. Bit like searching for LTE maybe.

 

[P_Watt]

That makes sense. Bit like searching for LTE maybe.

Got a refund, charger in trash.