What is the latest battery firmware version?

I'm not sure what the version number is, but when you do the firmware update on the drone, it will do a battery update as well if one is available. If it does do one, power down the drone and swap to the next battery out of your fly more kit and on the main screen of the DJI fly app, it should tell you that there is a battery update available. You have to swap the batteries around for each battery to update the bat firmware, The last couple of FW updates for the air 2 did not offer a bat update.