I assume you are looking for a simple parallel install to double available amperage and keep 12 volts. If so, simple short battery cables in the 2,4,6,8 range are available at most parts stores for short money. Just make sure you go positive to positive and negative to negative. Our local autozone carries cables with ends for top terminal, and stud style. Most likely you have top and studs meaning you can just buy short say 10 inch cables with rings on each end, add them to the existing studs and connect to the new studs... cake!
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