How to Charge a Diesel Truck with Two Batteries
December 8, 2020

How To Charge A Diesel Truck With Two Batteries

Written By: ProSource Diesel

If you’ve just recently bought a diesel truck, or are unfamiliar with diesel trucks in general, you might be surprised to learn that they have two batteries. As the weather gets colder, it’s a good idea to get familiar with your two-battery setup and find out how to jump-start or charge your truck batteries if they die.

Why Do Diesel Trucks Have Two Batteries?

The short answer is that diesel engines have higher compression and more resistance than gas engines. It simply takes more power to start them up. As an example, the normal compression ratio for a diesel engine is somewhere between 15:1 and 20:1. Gas engines are only around 10:1. A higher compression ratio means a more efficient engine, but it also means a higher resistance load, which makes the engine harder to start. Along with needing two batteries to get it started, the high compression ratio also requires sturdier parts. This is why diesel truck parts are constructed more durably than similar parts for gas engines.

Charging a Diesel Truck With Two Batteries

If your batteries die, then you can either charge them with a battery charger, or you can jump-start them using another vehicle. After the truck is started, you would simply have to drive for about 30 minutes until the alternator recharges the batteries. Let’s first take a look at how to charge your batteries with a charger.

The first thing to know is that you will need two battery chargers. One for each battery.

Step 1 – Disconnect the negative terminal on one battery, followed by the positive terminal. Repeat the procedure with the second battery.

Step 2 – Connect the positive clamp of one of the chargers to the positive terminal of one of the batteries. Attach the negative clamp to the negative terminal. Repeat the process on the second battery with the second charger.

Step 3 – Set the chargers to charge on low amperage. This will take longer, but you’ll have a more complete charge.

Step 4 – Turn off the battery chargers after two hours and try to start your truck. If it doesn’t start, use the previously mentioned process to reattach the chargers and charge for another hour.

Step 5 – Reinstall the battery terminals by starting with the negative terminals.

Jump-Starting a Diesel Truck With Two Batteries

If you don’t have time to wait for your batteries to charge or your batteries have died away from your charger, then you’ll need a jump-start. In order to do this, you’ll need a second vehicle that is running and two jumper cables.

Step 1 – Turn on the heaters of both vehicles, but turn all other electronics off, including the lights, stereo, windshield wipers, etc. Turn off the engine of the running vehicle, engage the parking brake, and put both vehicles in park or neutral.

Step 2 – Attach the jumper cables to the dead battery with the thickest cables, if possible. If the cables are the same thickness, then it doesn’t matter which one you attach the jumper cable too.

Step 3 – Clamp one jumper cable to the positive terminal of your chosen dead battery, and then clamp the other end to the other vehicle.

Step 4 – Attach the second cable by starting at the other vehicle’s negative battery terminal. Ground the other end of the second cable by attaching it to a piece of solid metal on your truck.

Step 5 – Start the engine of the other vehicle, then start the engine of the dead vehicle. Let both vehicles run for a few minutes. Shut off the engine of the other vehicle.

Step 6 – Remove the grounded cable from your truck first, then remove the cables from the positive terminals of each vehicle. Remove the cable from the negative battery terminal of the other vehicle.

Step 7 – Drive your truck for about 20 to 30 minutes to let your alternator charge the batteries.

If you need to change the batteries in your diesel truck, make sure to change both batteries at the same time.

Rely on ProSource Diesel for all your Powerstroke parts, Duramax parts, and Cummins parts to keep your truck running great for a long time. Whether you’re a do-it-yourselfer or a diesel mechanic, ProSource is where repair shops shop for reliable and hard to find diesel truck parts and kits.

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  1. Joel on December 15, 2020 at 9:38 AM

    Step 5 should install positive wire first and not negative. Negative wire is first off and last on.

  2. Colin Counard on December 16, 2020 at 3:02 PM

    Thanks for the information it will come in handy

  3. Thomas Nosterud on December 20, 2020 at 10:28 AM

    When disconnecting battery cables you always start with the ground cable first. If you have two batteries in parallel you would disconnect the ground cable of the other battery before touching the positive cable on the first battery. The reason for this is: if you happen to make a connection between the frame of the vehicle the positive cable there will be major current flow coming from the other battery (sparks).
    When reconnecting the batteries you always start with the positive cables (non grounded) of both batteries and end with the negative (ground) cables. Also to inadvertently grounding out one of the batteries. Especially after charging because sparks and hydrogen gas from charging makes for big booms. Not good when acid is involved.


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