Wired Ring 2 does not trickle charge

Hi. My son and I both have Ring 2 doorbells hardwired. His is about 6 months older than mine and the trickle charge keeps the battery at 100%. Around the beginning of this year, mine no longer stays charged. Thinking it was the battery, I installed the spare battery that my son had purchased but never used. It immediately started losing charge on a daily basis. It lasted about a month and then I put my original battery back in and it lasted about a month.My original doorbell uses a mechanical hammer and bell so I do not need the diode.Our doorbell settings are the same and have minimal notifications.Why does my battery not stay charged?Thanks,Joe