Doorbell 2 not staying charged

I’ve had my doorbell 2 for almost 2 years now, and it always stayed charged bc I have it hardwired.. however, I’ve had to unhook it twice now and charge it because I got alerts saying it was below 10% and it’s not trickle charging anymore like it’s supposed to. I verified I still had voltage at the doorbell. Is this a common issue? How can I fix it? Do I need a new battery?