RC car battery charging with the Prius

Recently I've gotten back into RC cars (mostly just offroad stuff for fun) and I have successfully been able to use the jump battery leads (or lead rather, since there is only a + terminal there). This is the one that's located under the hood and used for jumping the car should the auxiliary battery ever fail.

But I can report it works great for running the 12 volt DC battery chargers for RC cars, planes, boats, etc. But one thing that makes the hobby less fun is waiting on the batteries to charge. Even if you have 2 batteries in rotation so one can charge will the other is in use, you burn through a battery about 3 times faster than it takes to charge one (at safe max charge limits) so you have to wait for some time for the next battery to complete charging.

So I was wondering if I could run 2 battery chargers at the same time on the Prius? Since it has the jumper terminals in the front of the car, and the auxiliary battery under the trunk, perhaps a charger could be hooked up at both locations? Does anyone know if this is possible? I may try it to see if it works, but I also don't want to cause any damage to my Prius foremost, and to my RC batteries and charger secondarily.

Anyone more knowledgeable on such subjects than myself care to comment?

Cheers,
Powers.

 

Actually, I tried that and it didn't seem to work. Not sure if I did it right, but I just connected the + aligator clips to the positive terminal under the Prius' hood, and the negative clips to the body of the car as I normally do to ground it for the negative terminal. But then neither charger worked. I am attempting to draw 4 amps from each charger. And I am leaving the car in Ready so my main Prius battery never gets too low. Am I doing this correctly? Should this work?