With the final XT60 panel mount housing arriving yesterday I’ve been able to complete my ‘Flying Field’ charging pack 
It started life as a 12S 1P Samsung module for a PHEV. I’ve reconfigured it to 6S 2P and provided both a 6S and 3S output connector (3S 'cos my balance charger, a UnA9, only likes <14v)
In this configuration it gives me 74AHr which will charge a lot of 3S 1400mAh FPV packs 
I put in a substantial balance port as this will be the primary method to re-charge it.
It weighs much less than the car battery I was carting about and with it’s proper handle is a damn sight more comfortable.
Cheers
Steve