[bob]

My Duramax has duel batteries. My question is, when starting do both batteries assist in starting or does one battery assist the other? I know if you stack batteries the voltage also stacks. Whats going on under my hood?

 

[Premo Services]

I have a dodge-commins combo and it has two of the biggest battteries that I have seen in a pickup. I think the batteries assist each other, because the beasts are hard to get going when it is cold out. Also right after it starts and it is real cold, the grid heaters kick on and this will send the amp meter down for a couple seconds. I imagine they need two to do the other work batteries do also.

 

[UNISCAPER]

Two batteries are wired in series so the amperage increases during the start period. Some Ford and GM gas ttrucks also used this system. In larger diesels, they are wired in parrallel so the voltage is increased to 24 rather than 12.

 

[GLS]

Two batteries are wired in series so the amperage increases during the start period. Some Ford and GM gas ttrucks also used this system. In larger diesels, they are wired in parrallel so the voltage is increased to 24 rather than 12.

I think you might have the two backwards. Hooking batteries up in parallel (+ to +, - to -) will keep the same voltage, but double the reserve capacity.

 

[greendave]

GLS has it right. Parallel = same voltage, more cranking amperage. Series = higher voltage, same cranking amperage
It takes a lot of power to crank over a high comression (diesel) engine. Don't worry, within the next few years we will start seeing 42 volt cars and trucks on the road. All the electronics and electrical accessories on modern vehicles has outpaced the 12 volt system. That's why we went from 6 volt to 12 volt systems in the '50s.......