Originally Posted by
duncan333
Sorry to chime in at this late stage.
I have a 24v motorguide with the two batteries bolted into the boat and have connected them via a 3 pole/3 way switch. I can have them disconnected, in series (24 v) connected to the motor, or in parallel for when they are being charged and optionally (via another switch while in 12v mode) connected to the main electrical system for charging via the alternator or as use as the secondary battery overnight (lights, live bait tank) etc.
To charge I usually put the batteries in parallel (via the 3 way switch), and connect them to the starter battery. I have an anderson plug to connect the 20amp 12 charger.
This way I charge all 3 batteries at once.
If you are interested I can provide more details.