on the charger it will have a little diagram with an open circle with a dot in the middle and a line coming from it. on the end of this line will be either a + or - totell you which polarity it is. in the instruction manual for the radio gear there should also be one of these diagrams. as for the voltage I can't remember off the top of my head & I don't have my charger with me. you local hobby shop should have a range of chargers that are designed for this purpose that are pretty cheap, if you took the radio in with you they should be able to work out what you need. get a recharge switch & battery pack for the truck while your there, then you can plug the car & truck in with the one charger the night before & they will be ready in the morning. I make my own battery packs. cheaper (less than 1/2 price) & easier.