I'm another vote for the 2 batteries parrallel for the 12 volt system, the biggest you can fit. Better suited to what you're doing is the 24 volt system and you'll never need to upgrade again. The initial cost was tough for me too. 6 years ago. And short of just wearing out a set of batteries I've never had to do anything but use it. I bought a pro mite series charger from BPS and just upgraded this time to 2 - 29 series batteries from Wally for just under $200, and never wear em down in 6 hours plus of pulling a heavy bass boat around. Do it once, do it right, and you'll not regret it.