I have a P4P v2 and keep getting "battery not installed" on all my batteries (2). The drone/batteries were purchased in 2018.
I just received a new battery from B&H and it is also giving me the same error. I have updated my firmware and DJI assistant to the latest version. Is there anything I can do to fix this error?

check and clean with a fine brush the connections, both the battery and the drone

Rather than the electrical connection, that sounds like a problem with the sensor that detects whether the battery is properly fitted.
It's a feature that is only found in later versions of the P4 pro.

Hello there. I am sorry to read and to know that you are having issues with your DJI Phantom 4 Pro v2.0's Intelligent Flight Battery.  In order to ensure that the battery has been installed correctly during use, DJI Innovations has a detection device for the battery installed in place in the battery compartment. Kindly please first check whether the intelligent flight battery is installed and the buckle is in place, then please try to wipe the metal paddles on the battery and the paddles in the battery compartment with a dry paper towel. If the problem still persists, it is recommended to contact our support team at http://www.dji.com/support for further assistance. We'll do the best to help this out. Thank you.

Battery not installed properly. Unable to take off. Check and re-install battery

djiuser_54f4smbQbQxr Posted at 10-1 20:21
Battery not installed properly. Unable to take off. Check and re-install battery

Hello there. Sorry about the inconvenience. Do you have an extra battery to test if it will show the same error?