I have no knowledge of welding so please don't assume any of the below is correct! It was just based off of the above video....
I have a 12 volt jump start battery pack i figure i could carry for the 3rd battery (main + dual+ jump start pack) if i wanted to do this solo...would need some of the other random welding stuff i just don't have (not a welder :-( ). Anywho...here is the list i came up with: