Doorbell 3 Plus - Hardwired won’t charge to 100%

Have hardwired 3 plus, battery drops to below 90% and then starts trickle charging again, as it should. However, the battery never seems to get above 99% though and then begins to drop back again. My stick up cams charge to and stay at 100% for some time before they drop again.

Any ideas?

@Chris0576 This is normal behaviour.