I see Micah solding #10 wire on the battery build kit. What's the trick? Pb solder will not wet the metal strips. I've tried rosin core solder with and with out flux, forty watt and one hundred watt soldering irons, I've tried a gas torch. The metal gets hot enough to metal the solder, but the solder always balls-up and rolls away.
Soldering to the V1.5 bus bars can be tricky, as they are SS. I sometimes experiment with different types of rosen core solders until I find one that works well. Another option that people sometimes use (which avoids soldering altogether) is to use ring terminals for the wires, and then just crimp them on the wire and bolt them onto the terminal. You could also solder them instead of crimping them. And since they are usually tin coated copper, they solder much easier.