Here's how I have the batteries wired:

The first picture shows the XT90 connector. That takes quite a bit of heat to get a good solder connection with the 10AWC silicone covered wire. This wire is super flexible, very nice to work with.  I'll add a link in components.

I have 3 separate connectors, and plan to have 2 banks hooked up at first, and by switch (and contactor from a Toyota Prius) change over to the backup bank. I don't want to be out of power before I have time to crawl back up on the back of the truck. If you look at the battery connections, the square post is negative and the rounded side post is positive. The copper straps and screws came with the battery pack, nice all included package. Purchased from the local salvage yard ... I got 2 Honda Accord batteries like this one, 2 Prius batteries (these include high current contactors) and a Ford Explorer hybrid battery at 330V ... all from the local salvage yard, all for $40 and a dance (yes, I actually danced). The total weight made my Jeep Wrangler sag a few inches.