I have got my Mavic Pro with the 3 battery pack. I have managed to upgrade two of the batteries, but not the first one that I inserted onto the Mavic.

I initiated the FW upgrade by following the prompted instructions in the APP, and it got stuck in the middle of the upgrade for at least 45 minutes. It indicated something like "Battery Level is under 50%". Then I unplugged it and plugged in another one that was fully charged. And it went through. (I have got two of the batteries ugraded as aforementioned)

However, the very first battery which attempted to upgrade is bricked now. Sitting here with the middle two lights blinking with an interval of 15 seconds approximately. What should I do now?

Put the battery back into the Mavic and then use the Assistant 2 software on a PC to update the battery.

Thanks Jenee 2, that did the trick for me, I had the same problem.

Kenneth R. Posted at 2017-8-23 00:26
Thanks Jenee 2, that did the trick for me, I had the same problem.

Also once the FW update is installed and everything powered off then powered on again any additional batteries mounted to the Mavic should update automatically  using the new FW

Have a look at this post.
The poster claims that he has found the solution:
https://forum.dji.com/forum.php? ... &fromuid=863102

Like Jenee 2 mentioned, please upgrade this battery via DJI Assistant 2 again. But you need to make sure that the battery has enough energy for upgrading, if it might be insufficient, you can keep the battery in charging for about 2 hours. The middle 2 LED lights will keep lighting and the power button of the battery will not work until the upgrade is successful.