Ring video Door Bell Hardwire Charging

I purchased a Ring Video Doorbell the other day and hardwired the unit. After 2 days I saw on the app my power status had gone from OK to Poor. clicked on this to see the battery was 36% and decreased throughout the night to 31%.Now it was frosty so I wanted to check if this was normal even when hardwired?I took the doorbell off and gave it some charge (didn't let it get to 100%).Installed this with 46% charge this morning but its not seemed to have gone up since wiring it back up to the door.Shouldnt the HW be charging the battery through the day?