He would just need a jumper from one battery to the other if im following him correctly also. Btw.. buy your stuff from walmart lol.. i buy there best battery.. its a 2 yr warranty. I just switched them out.. and they ended up giving me back money lol
If you just add a jumper from POS to Batt 1 to NEG on Batt 2 you will get 24v...that is a series circuit.