Have an idea but need some input ...
item 1)
Lets say you have a vehicle with two batteries and they are both charged by the same single alternator. HOWEVER, the batteries are isolated from each other by diodes in the charge wires from the alternator.
What happens if one battery has a full charge and the other does not ? The regulator in the alternator will want to charge the low battery. But what happens with the other battery - would it be damaged from the continuous charge?
item 2)
I've heard of "coil saturation" and I know that very often ignition is left "on" without cranking the engine. In these cases what stops the coil from literally exploding?
Item 1 - Your batteries wouldn't be very useful as the diode would allow current to flow from the alternator to the battery, but no flow out of the battery. Both would be charged at the same rate though. There would be no way to completely isolate them from each other if they are going to feed the same electrical circuit. Now if one was just a starting battery and the other handled the rest of the electrics, then yes.
Item 2 = the coil winding would most likely burn out before the coil exploded. In a points system the coil is only energized if the key is on AND the points are closed, not 100% sure about electronic ones though. Coil saturation is something different, it is, essentially, when the coil's magnetic field is completely built up and can grow no more.
