Argus Pro 3 - Worked fine outdoor for years, now loses connection as soon as it's unplugged.

As described in the title.

Connected via WiFi, but bringing it indoors doesn't help. Works absolutely fine whilst plugged into power or while sun is shining on the solar charger. As soon as that stops, the camera stays on but the connection instantly drops and a red flashing light appears on the front.

Have tried deleting from the app and readding it, etc. No joy. Any ideas?