Hard wire doorbell gen1

Hi, so I’m trying to hard wire my gen one. I’ve got a plug and has the connectors to be screwed on. But this is a gen 1 so they get fitted to the back plate and then the doorbell connects on the plate and should charge. But it doesn’t. Do I need to do anything in settings or remove battery? The power supply and plug are fine as I tested it with my neighbours gen 2 and chargers it no problem. I’ve also disconnected and swapped them over still nothing.