Basically, the interconnecting cable in the series pairs should be at least as large as the outgoing power leads. There is nothing wrong with having larger cable connecting the pairs but you should never have it smaller than the power leads. The same is true for the parallel connection cable.
If you are using a larger inverter, you should have larger cable that is rated for the amperage load of the inverter draw. Be sure to use a fuse or circuit breaker for circuit protection of the power leads. I like to use a large amperage catastrophic fuse attached to the positive battery terminal for that protection. I am basically protecting the cable in the event of a short.
Genuine deals.com is used by some Forum members for constructing and supplying cables. There have been favorable reviews of that company.
