I have the same problem with my newly purchased Gen 1 solar charger. At first it seemed to be working and the battery charge stayed above 90% and was beginning to creep up over time.
Then I went away for the weekend (when there were actually no motion notifications due to a lack of visitors), and when I got back the battery is suddenly at 27% and it’s asking to be recharged!! In the device health screen it says the charger is “Established”, whatever that’s supposed to mean.
It’s on a South facing wall and gets several hours of direct sunlight every day. I’m pretty unimpressed at this point. I guess I’ll charge it up again and see what happens, but if it keeps failing I’ll have to send it back