Golf cart batteries vs storage vs charging??

evy wrote:
In order to plug the trickle/smart charger on the batteries I need to convert them to 12 volts, I need to buy a short wire to do so, is 4 gauge big enough? and which terminal do I use? the threaded one or the bigger one? from what I see on google image most people use the threaded one.

For the trickle charger, pretty much any wire will do fine since the current is small (an amp or two at most). Look at the size of the wires from the trickle charger for a rough minimum guideline.

For eventual use in your van, the interconnect wire should be sized based on the current required by the van (or put out by the converter) in the worst case. Basically, that boils down to having it be the same size as the ground wire and the positive wire, assuming there's only one positive wire connected. 4 gauge would probably be fine if you don't have a large inverter. One or two gauge ought to be sufficient in most any case.

It doesn't really matter which terminals you use; whatever works for the terminations on the connecting wire. Most do use the wing nuts because most RVs have wires with ring terminals on them. The posts may be a little more secure if you have the proper size of clamp for the post, but both are satisfactory.