First gen doorbell hardwire.

I have connected a first gen ring doorbell to an ac transformer via a 25 ohm resistor. There is no mechanical chime in the circuit. The terminals on the mounting plate measure 20vac, but After 24 hrs the device still shows battery and the charge level is still dropping slowly, currently at 63%, was 65 when I connected it. Does it like to discharge to a certain level before topping up and changing to hardwired status, or is something else wrong here? It’s a 9va transformer.