ORIGINAL: CGRetired
That looks pretty good. The only concern for those that would think about something like this, is to make darned sure the switches are capable of handling the current that will flow through them. If it were me, I'd get something that was at least 50% more than what you figure you will need. For instance, if your current draw is at about 20 amps, I would definitely make sure the switch can easily handle 30 amps.
Just remember that series devices are ''voltage'' devices in that the ''available'' current remains the same but the voltage is a factor of the number of cells in series, where parallel devices are ''current'' devices in that the voltage remains the same no matter how many cells you have where the current available is a factor of the number of cells in parallel.
CGr.
About 6 years ago my partner did a 24 volt two auto batteries like this fellow so his Dynatron starter would roll over his G-40 {38?} Didn't have the switch for 12 or 24 though, just series. With the money he spent on the starter and two batteries he could have just bought one of the good geared starters everyone was selling back then. Small and only 12 volts like any other starter. The problem with two batteries is lifting and carrying. Back then I could do it and my partner was younger and stronger. Thesd days we have the small drill batteries to use.