Ring doorbell(2nd Gen/2020 Release) slow charging and hardwired

Hi, My ring doorbell(2nd Gen/2020 Release) charges slow and is hardwired. I have been observing for several days, no doorbell event(Ring Alerts), there were about 3 motion events and 2 live-views every day, and the snapshot frequency is "Every14 minutes". Battery charging can only increase by about 10%(It probably stays at around 80%, Can't be full. It stayed at around 70% when snapshot frequency was "Every 5 minutes" ). PowerSource shows "Hardwired". SignalStrenth is "RSSI-59". Firmware is "Up to date". The same hard-wiring (24V AC) used to work well with the first-generation ring doorbell. Any idea? Thanks.