I want to charge my batteries in parallel instead of one at a time.

Hello there. Good day and thank you for the inquiry. I hope that you will get the best recommendation from our fellow DJI co pilots who have done this process in charging there DJI intelligent flight batteries. Just a reminder that there is a possibility that these 3rd party chargers will be able work. But however, since it's not yet optimized and tested by DJI we cannot guaranteed the stability of the said 3rd party chargers if it will charge the said batteries all the time with no issues and using 3rd party chargers might void the warranty of the said DJI product. Thank you.

This is copied from another reply:

I haven't used the supplied battery bar in months. I use this device that you see in the video at the 13:10 second mark.  It works faster better and simultaneously as far as the drone batteries are concerned.

Plugging your goggle battery into any USB port and then plug in the C port will charge them just as good. They also make an adapter that will allow you to use almost any lipo battery to power the goggles.

https://www.amazon.com/gp/produc ... 0?ie=UTF8&psc=1
Don't get hung up on the supply battery