When I first did the firmware update everything worked fine as far as the download went. I have had the usual spate of problems no map(fixed), IMU needs calibrating(not fixed), Jerky flight (not fixed), camera shuts off (not fixed), etc. I decided to check on assisant II and do a reinstall. When connected it showed I again needed to update the firmware. I did the update and realised I needed to update with all my batteries and originally I only had done it on one. I had not seen anything in the updates about this. When I use two of the batteries I get the IMU warning on the other its fine. I'm just throwing my experiance out there. I don't trust my drone anymore on flights, (I live with a lot of water). I can only wait and see what is going to happen with a fix on the other side. I have tried every fix I could find.

Firmware update is required when the aircraft firmware and battery firmware not matched. Please make sure all batteries have been updated to the latest one and check again.

Are all battery the same 5350mAh or 5870mAh ?

Mine are 5350mah All my batteries are now properly updated to the new firmware. Still won't work right but I did all that was asked. There was no mention of this by DJI, app or otherwise. The last time there was battery update it showed nicely in the app. Disappointed I am as I love my P4 and now I can't trust it.

Are batteries only updated via a direct plug in from iPad to drone? I have 4 batteries, how do I update all 4 of them?