Hi I purchased my Phantom 4 Brand new from a retailer in Newcastle NSW in April 2017. All was fine until I did the firmware upgrade on 7.6.17 version V02.00.0106. The Copter is still under warranty and nnever been crashed or damaged. Since the upgrade, during flight, I get a battery error message on the remote. The LED's go to solid red. Everything is ok prior to take off, green led's flashing, IMU etc. but battery error comes up and flashes intermittently. Copter seems to fly ok but how do I know something wont happen unexpectedly when that is flashing on the remote. I contacted DJI support and they suggested discharging the batteries completely and recharging. If it doesnt work send back the batteries? Its sounds like a stab in the dark and not a fix just a bloody inconvenience considering I paid $2K for this machine less than 6 months ago. Anyone have any suggestions or experienced the same problem?

Return the whole package back to the retailer as it's still under warranty and exchange it for a new one, there's no guarantee it isn't going to drop from the sky. It's the retailers responsibility to sort it with DJI, that way you won't be without your drone.

I assume that's not a spare battery, there was an update to batteries as part of the process. But if battery is faulty then sooner returned the better, DJI only cover them for 6 Months. Although you may be covered by retail law in AU.

Previous posters are correct in that if you think you're having an issue with your battery, it's only covered for 6 months so factor that timeframe in if you decide to get it sorted under warranty. Also, if you can get your hands on a second battery in the meantime, it'd be interesting to test that in your craft to see if you still get that message.
As far as the craft goes, if you haven't already, try setting it to factory default (using Assistant 2), and refresh the latest firmware at least TWICE, fully power cycling in-between. There have been many issues with this latest firmware which suggests that various drivers aren't being applied successfully during update.

Apologies for the inconvenience first. I would recommend you to report the issue to your dealer or connect our Support Team via support.au@dji.com, they will take care of it.