I use power banks that are shells for 18650 batteries.
I always called these "lipstick" batteries. I don't think they have enough circuitry to shut down. When I started using bigger packs, I was a bit surprised that my garmin would act like it wasn't being charged, because I would plug it in when fully charged and the pack would shut off.
It's a technical challenge to design a current controlled circuit to be stable from zero current on up, so I suppose I shouldn't have been surprised that they refuse to charge at lower current draw