Originally Posted by C2 RIBS
Stevo- If this has been rigged sensibly then by putting the switch on both the engine will charge both batteries and should charge No 1 first and then No 2.
Not with a standard battery switch. Switching to "Both" will connect the 2 anodes together, and connect the 2 cathodes together, creating what is in essence a double-capacity battery. Any charging or discharging will affect both batteries simultaneously (assuming the batteries are in usable conditions. If they're not, you'll attempt to charge the bad one, and the good one won't receive the voltage necessary to charge.)
Even with an isolator, selecting "both" will parallel the two batteries.