MDI Mainer wrote:
A similar issue has appeared after some firmware updates, but is more commonly related to third party batteries.
https://shuttermuse.com/sony-a7iii-battery/#:~:text=It%20will%20say%20%E2%80%9CThe%20operation,indication%20of%20the%20charge%20level.
This from the article:
Note: If you receive this warning on the screen even when using your original NP-FZ100 battery, it’s a sure sign that you actually have a counterfeit!
My thoughts also. There have been reports of counterfeits infiltrating the supply stream.