I have a heavy duty 6 ton truck with 24 volt start batteries. I am building a house battery system, also 24 volts. I want to connect the house battery to the car battery with a switch, so that I can use the house battery in conjunction with starter battery when I use the diesel heater which is connected to the starter battery from factory.
The truck has a big old engine and hence a big old 4kW alternator. I have been warned by a person (not sure his opinion is correct which is why I'm asking here) that if I connect my house battery to the car battery and crank the engine, the voltage spike could burn up the cabling between house and starter battery, unless it is of the same gauge as the cable from alternator to start battery.
Does this sound correct? From my understanding electricity takes the fastest route which is through the thick 70mm² cables going from starter to starter batteries. Cables between starter battery and house battery are AWG 12 and hence the draw on the house batteries when cranking will be less.