Well this is what is use at the field
I have a Ford 250 7.3 diesel, it has two LARGE batteries up front, I ran a 6 gauge wire from a dedicated fuse, close to left front battery, the wire runs down through protected sleeves clear to the back corner of my pickup box. I have a electrical box mounted there and have 2 sets of banana plugs, Deans plug, XT60 plug, and I am going to add a cigarette lighter plug. I use a slide out in my truck as my model/flight bench at both of the fields I fly from.
I have 3 model chargers mounted on a piece of plywood about 8" X 24". One is a Hobbieco Elite, a Hobbieco Fast Field charger (both of these are dual output chargers and multi type) and a Astro flight 109 lipo charger. I can charge 5 at once if I had enough balancers. These are all wired to a common bus, and it plugs in with one cord. The Astro 109 has a input voltage readout, so I always know how my truck batteries are holding out.
At home the charger board plugs into a 13.3vdc ,11 amp output Astron power supply. I'm not in much hurry at home, so the 11 amps is fine. The truck could deliver 60+ amps.
Any portable battery to use at the field will have to be very large to charge your batteries for a week end. I can simply start the truck for a little while if I get down to far, but so far I have been out all day flying, and could not tell any difference when I started my truck.
We would all like to have a 10 lb battery with about 1000 amp hours, or a portable nuclear power plant for those long dry camp sessions, but I can't find one, so this is my answer to my problem, your best answer may be different, but I hope it works as good.