Another option for you Buck
I put a deep cycle marine batt. in my van.. that is wired to a power inverter at the rear of the van
this gives me 110 volts at my field... I can dermel, use the radio and charge
I run a extension cord over to my table and plug into my power supply then to my chargers

I've been asked many times why I have an inverter going to 110 then a power supply back to 12v

the reason is I can run a long cord to where ever I'm setup on a table at the feild and not have my chargers in the dirt next to my van..
it's also nice having 110 at the field.. last weekend I was getting wrinkles out of a wing with my heat gun and the guys thought it was pretty cool..

Oh and I do have to run the van while I charge... I run it all day and the gas needle doen't even move... it's also nice that you can't hear my van while it's running
generator are pretty loud

my jets and planes run on two 6s 5000 mha pack in series with two 1010 charges I can charge two packs from 80% dead to full in 35 minutes

Ron