Charging a garmin 66i with a powerbank

My 66i chargers normally with a power wall socket. I plug it in. The device comes on. I push the power button and then the battery indicator comes on and it stays on display until 100 percent charge.

It behaves differently with a power bank. I plug it in. It comes on. When I push the power button it displays the battery charge and then powers off.

Anyone else have this issue.

Is it OK to keep it on as it chargers?

Or does it still charge when powered off

Or do I have a problem?