Wire Size to Connect 2 12V Batteries?

We just rewired my house battery to engine battery/alternator connection - it was about 10-12 gauge. Used 4 gauge wire throughout. Since we were adding circuit breakers into the system, I went to Battery Bill and they cut the wires to size and added all the appropriate sized lugs to each end, and heat shrinked them with the appropriate red/black colors. Cost was only $1.85 per foot.

X3, pre-made battery cables from virtually every auto parts store, even Walmart carries a few varieties.

enblethen wrote:
I would get the ready-made battery cables. Most are #4 from your local auto parts store.

X2

I would get the ready-made battery cables. Most are #4 from your local auto parts store.

When Winnebago installed my two batteries, they used 1 gauge wire. When I replaced them I used 2/0 wire.

That being said, Winnebago used 8g wire to carry all of the power between the batteries and the converter/RV. I also upgraded that to 4g wire.

The heavier the cable, the better, and good quality terminal rings, like these;

Heavy Duty

My thinking is 4AWG cable being so much available and does not coat all that much I use this gauge for all my two up to four battery wiring projects. All of my wiring uses the appropriate sized ring terminals. I always use equal lengths when wiring is used together for like connections.

I buy 25-foot spools of Marine Grade ANCOR cable purchased from EBAY STOREs for around $50 and cut my own DC cables. I also use a 8-ton hand crimper and adhesive heat shrink ends when using the ANCOR BRAND Ring Terminals. All of my 12VDC connection use the battery component stubs just about everywhere.

I also use BLUE SEA HD Switches, Terminals, Fuse Blocks, etc for all my 12VDC projects.

This allows me to make changes when needed and not have to do the wiring all over again...

Roy Ken

The same size wire as the leads to the RV will be excellent.

This is what is balanced and best for twin twelve volt batteries.



As it often doesn't cost a dime more to do this, I think it is worth the trouble.

If you wish to understand the "why" surf here:

correctly interconnecting multiple twelve volt batteries

Others may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?

Here is a video of 3 twelve volt batteries that have been wired in an unbalanced manner for 2 years. They have been equalized. The test shows how CCA has been adversely affected.

unbalanced for 2 years

why not just use 6?

RJsfishin wrote:
The wires need to carry 1/2 the current being pulled from both batteries. It is probably ok, but why not at least 6-8 ga for the interconnect

X2