Don't know what the wire gauge is, but I've made cables from welding cable. I was able to get some at the local hardware store by the foot. I like the welding cable since it has a high wire count making them really flexible. I fashioned some cable ends using copper tubing, I believe 5/16", by flattening one end of a 2" piece and then drilling holes for the battery terminals and the end bolts. I then soldered them on using rosin flux, solder, and a torch. Then I used heavy-duty heat shrink tubing to finish them. It's been almost 10 years and they still look and work great.
