We just got back from a 1600 mile trip from California to Utah and back.
My brother in law's 2002 truck had one of the batterys go completely bad.
We took the bad battery out and the truck works fine, starts great without
problems.

Here is the question: In moderate temperatures such as California, do we
really need to have the extra battery on our trucks? :rolleyes:

I'll guess that when it's sub zero and you want the glow plugs to heat it up before starting plus cranking to start, you need the second battery.

I was doing the recondition thing with my new charger a few months back by disconnecting one battery at a time. Mine started fine also. I am not sure at what temp the glow plugs and heaters work but even in summer here they come on first thing in the morning. I didn't check to see how much one cycle took out of the battery. It will definitely pull one battery down more and would take longer to bring it back up. Later! Frank

All the guys with twin turbos are only running one battery. I think if you aren't in a cold place you are ok.

I was told by the guy that does my generator maintenance (diesel) that the truck only uses one battery for the motor. I always thought that the two batteries were necessary because of the extra load the pre-heating added. What really made me question it was when he started telling me that he had a Duramax and we started talking about the motors. He told me that the second battery was for trailer lights, etc. He said that all of the generators that he maintains only have a single battery, and that it was all that was necessary to start the diesel engine. I also started thinking about it when both of my battery(ies) were dead after letting the truck sit for 3 weeks, with just a flashlight charger hooked up. I would think that with two Optima deep cycle batteries in there, that they could provide power to a flashlight charger for 3 weeks and not be totally dead.

Maybe I'll do some more searching now and see what I come up with.

Swamp Monster, he doesn't know what he is talking about. Both Batteries are in parallel with no isolator. They are both doing the exact same thing.

The one truck with twins I've seen still has two batteries - one's in the box. I wouldn't be running around in the winter up here with only one.

When I was installing a stereo, the posts broke off the drivers side battery. I took it completely out and the truck started up like normal. I drove to town and got a new battery.

The one truck with twins I've seen still has two batteries - one's in the box. I wouldn't be running around in the winter up here with only one.

I do agree you need it in the winter to crank the motor with heavy oil in the cold.

Sp33d said he is running one optima red top for now though.

It will start with one battery, but with the voltage drop the starter won't last very long.