Nest Cam (battery) must be connected to a power source to have 24/7 video history. If you’ve connected them to a solar panel, the panel doesn’t directly power the camera. Instead, the battery is trickle charged by the panel, and the camera still runs off the battery charge. Because the power source isn't continuous, it's not considered to be connected to a power source. Definitely appreciate these finer details can be frustrating, however there's no way to override the way this works. I'll link the relevant documentation below.
Cold weather battery charging behaviour in Nest cameras and doorbells - Google Nest Help
If you’ve connected your Nest Cam (battery) to the Wasserstein Solar Panel, the panel doesn’t directly power the camera. Instead, the battery is trickle charged by the panel, and the camera runs off the battery charge.
Event and 24/7 video history - Google Nest Help
The Nest Cam (battery) must be connected to a power source to have 24/7 video history. If your camera is battery powered, it will only have event video history, even if you have a Nest Aware Plus subscription. 24/7 video history is not available for the Nest Doorbell (battery), even with optional wired installation.
