gage wire question

I want to add another battery to my existing trolling battery not sure what gage wire
to use. basicly pos-pos neg -neg. running a mk 40 lb. trying to get more runtime.

thanks

You can buy battery cables at your local auto parts store. They come in different lengths and I believe they are 4 gauge.

6 would work 4 would be better. Go to parts store and get 2 battery cables that have ring eyes already installed on each end. One red and one black. Cheapest and easiest way to do it.

thanks guys

If batteries are next to each other, I don't think there is any reason to go any heavier than 8 ga.