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Discussion Starter · #1 ·
I don't know if all Duramax diesels came with two 12 volt batteries, but my 2018 GMC Duramax 2500 came with two batteries. My question to those with jump starting experience is; Can you start this engine with one 12 volt fully charged car battery, or do you have to have two batteries and two sets of cables ??
 

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You can just attach cables to one of them, usually the passenger side since it has the positive stud sticking up. The batteries are wired in parallel so both will charge at the same time. Two batteries in parallel gives you longer charge time.


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I don't know if all Duramax diesels came with two 12 volt batteries, but my 2018 GMC Duramax 2500 came with two batteries. My question to those with jump starting experience is; Can you start this engine with one 12 volt fully charged car battery, or do you have to have two batteries and two sets of cables ??
the batteries are in parallel, so connecting either battery to a car with cables will connect both batteries to that car.
 

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Warm weather, you only need one 'good' 750cca or more batt to start the truck. Overkill with two is mainly for winter starts.

Depending on how the drain came about, consider this....

If you left something on and it did a slow drain, try to connect to the easier accessed pass side batt.

However, if it came up dead one morning out of nowhere, 1 of the 2 is probably on the way out and the other could no longer keep up the battle, joined to a shorted cell batt. (replace in pairs)

Majority of the time it's the pass side that fails 1st (dead air heat zone in the corner).

If that's the case, you'll have better success with a jump if you pull the neg cable off of the pass side batt, and jump the driver's side batt.

It'll probably work on either side with 1 failing, but if you still have a 'click' on a jump attempt, the bad one may be draining any amps via the jump cables before they can build enough to jolt the starter. So consider pulling it from the loop (neg-) and jump the driver's side.
 
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Warm weather, you only need one 'good' 750cca or more batt to start the truck. Overkill with two is mainly for winter starts.

Depending on how the drain came about, consider this....

If you left something on and it did a slow drain, try to connect to the easier accessed pass side batt.

However, if it came up dead one morning out of nowhere, 1 of the 2 is probably on the way out and the other could no longer keep up the battle, joined to a shorted cell batt. (replace in pairs)

Majority of the time it's the pass side that fails 1st (dead air heat zone in the corner).

If that's the case, you'll have better success with a jump if you pull the neg cable off of the pass side batt, and jump the driver's side batt.

It'll probably work on either side with 1 failing, but if you still have a 'click' on a jump attempt, the bad one may be draining any amps via the jump cables before they can build enough to jolt the starter. So consider pulling it from the loop (neg-) and jump the driver's side.


im going to disagree with you a bit here, and im not saying your way is wrong, just that there may be a way to do it without caring what killed what. The best way to jump a duramax is with the positive on the distribution stud near the alternator, inside the little red box connected to the wire harness, and the ground on the engine block. Keeps any sparks away from the batteries, and you have the shortest path for the starter to crank from. The cables are already adding 15-20 feet of extra wire path for the starting circuit, the closer you can get the cables to the starter the easier it will be to start the truck. This is especially true if the power donor is a car or gas truck with limited electrical reserves.

While you can jump it anyway you want and get usually good results, this is the 100% tried and true way to jump it every time regardless of the state of the batteries, unless they are completely shorted internally.

Going to either battery puts the battery closer to the donor vehicle electrically than the trucks starter, so the battery is going to get more of the donors starting power than the trucks starter compared to jumping it from the distro block. Since generally you are jumping off a jump box, portable jumper, or a car / light truck, and wont usually have the reserves of a diesel to jump from, its best to give the starter as much juice as you can. This is also why anything under 4 AWG copper cables should go in the trash, with 0 AWG being preferred.
 

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I agree, the post is a good spot (if you can get the large clamps from a decent AWG set to fit).

However, consider also;
The jump car system is going to be severely underrated to jump a Dmax on 1st try.

Hooking up a short run to the truck's (presumed) 1 good batt, and giving it some time to accumulate in the batt before a start try, will result in a larger kick to the starter, vs from jump car to the starter (via red box terminal).

But I guess if you hook to the red box block and wait to build, you'd have the same outcome? (unless both batts are toast)
 

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I agree, the post is a good spot (if you can get the large clamps from a decent AWG set to fit).

However, consider also;
The jump car system is going to be severely underrated to jump a Dmax on 1st try.

Hooking up a short run to the truck's (presumed) 1 good batt, and giving it some time to accumulate in the batt before a start try, will result in a larger kick to the starter, vs from jump car to the starter (via red box terminal).

But I guess if you hook to the red box block and wait to build, you'd have the same outcome? (unless both batts are toast)
usually you can crank right away at the distro point and dont need to wait for the batteries to surface charge, but if not, yea you can just let it sit there and charge off the donor. I tend to not like doing that because its a lot of load to put on a poor little honda go kart charging system, or whatever your jumping it from. The closer your batteries are to 100% dead the harder it will be to start, because the batteries will draw more current away from the starter. Both ways work, i have had noticeably better luck at the stud though.
 

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The worst jump off was with the side post batts....not enough contact area from the bolt head to the clamps surface.

I always prefer that the jump-from be engine off, using their battery storage.
Vs a feedback situation of two clashing alternators once the truck starts.
Their stored amps are more than their Alt would put out anyway.

I do the same if mine is the jumper.
"wait, you turned your truck off?"
"If 1700 amps from my pair doesn't make your KIA starter sing, the measly 145a alt churning won't make a diff!" :teehee
 

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Discussion Starter · #10 ·
Thanks for the instructions. I know that some day I will have to use this procedure!!!!!
 
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