I have this issue with my second battery doorbell. The first had a lot of connectivity issues and it was replaced. The replacement (brand new) had no issues and was charging fine via the existing doorbell wires/transformer. But after 6/7 weeks it suddenly stopped charging (no wired connection icon in the eufy app anymore). I’ve changed the wires, installed a new transformer but i’m not getting it charged. It chargers fine via usb (i waited with charging via usb untill it dropped below 40%).
I have exactly the same issue, and I checked with my trusted multi-meter, it is definitely being charged.
I even put a small AC incandescent light bulb to double check under load - it lit up.
Small update.
I tried charging my device to 95% via USB, then hooked it back up to the AC wires.
I now have the power cord symbol again.
I wonder if the AC charge method is unable to recover when the battery voltage drops below a certain threshold.
I never ever charged the camera - I had directly installed, so it could be the charge was never high, and with winter, maybe the charging system did not have much time to kick in.
We had a fair few days of -5 to 5 degC.
(Even though this last week was actually 5 to 15degC).
When it gets cold outside you can lose up to 40% of your battery efficiency. The AC trickle charge will help, but I always check the state of charge before cold weather starts. Do that by turning off the AC and waiting 30 minutes. That should give you the accurate charge percentage. If its below 70%, you can either charge it manually or change the power manager settings to reduce recording time in cold weather. That will reduce your current draw and allow the AC charge to keep up.
The AC charge will cycle once it gets a decent charge level. the cycle points depend on how many detections and how long you record. Last time I checked mine it was going from 60 to 80%.