Longest interconnect battery cables?

You can go to an auto parts store and get a made up cable to do this.

Typical cable will be #4, a 4 foot piece of #4 at 25 Amps will have a voltage drop of 0.05 volts. Unless you are planning to try to charge at some unusual rates, or run a BIG inverter, this will be more than adequate.

You don't talk about the rest of your wiring. If you are planning to tie this to a distribution panel located elsewhere, all the wiring lengths and draws need to be figured in. The size and drop of the jumper is no more or less important than the size and drop of the total wiring between panel and batteries and between the batteries themselves.

Doug

I agree with PAUL that you will need the cable connection between the two 6VDC batteries be as big as you can deal with. However a 4/0 cable is going to be a pretty large diameter and will be difficult to use. You will have to have your two 6VDC batteries mounted very stable and the large diameter cable installed in good manner to not cause stress on the battery terminals. The large diameter cable may easily rip the 6DVC terminals right out of the cheap plastic battery case.

Your two 6VDC batteries will give you around 220AHs of capacity and more important will produce around 25AMPS of 12VC current for 7 hours before discharging the two batteries to around 10.5VDC (0% charge).. You of course really don't want to drop your batteries below 12.0VC (50% charge state) to keep from doing damage to the batteries.

To get roughly the same results from two each 12VC batteries installed in parallel the TroJan T1275P 150AH batteries might be a good alternative. These two batteries will have a 300AH capacity and produce 25AMPS @ 12VDC for around 9 hours before getting down to the 10.5VDC (0%) charge state.

Using the 12VDC BATTERIES will allow you to use 4AWG or 2AWG batteries interconnect cables which will be easier to work with.

The difference is going to be cost of the batteries as the availability of the GC2 6VDC 220AH capacity golf cart batteries is around $80-$90 each. The Trojan T1275 batteries will probably run you around $190-$225 each.

Check the battery specs and get the ones that give you the most AH capacity and the best output performance rated in DC AMPs and minutes.

Just passing along for your food for thought process...

There are a bunch of GC2 6VDC batteries installs in the RV community these days...

Just my thoughts
Roy Ken

If I'm visualizing this correctly the two original batteries are in between this area right? So the distance from one of these new battery boxes to the closest original battery would be shorter than the distance to the other new battery box, correct? Maybe only 2 feet for example?

If that is true, then the best way to connect would be to pair up each new box with the closest original box.

If your current batteries are less than a year old and in very good condition you could keep them paired and move one to the nearest new box, then put two new batteries of the same size and brand in the other pair of boxes. Otherwise four new batteries are the way to go because weaker batteries will decrease the life of the new.

Happy Travels!

I would use #0000 (four ought) welding cable.

go to a battery store and have them make you a set and be sure you tell them what it is for so they can use the proper gauge wire.