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How to Jump-Start a Diesel Truck With Two Batteries

A heavy duty diesel truck with two batteries

If you recently bought a diesel truck, you’ve made a smart move. The upsides of a diesel truck are tons of torque, rugged construction, reliability and long life. Not much is going to stop that rig. Except maybe a dead battery. Avoid getting towed or stranded by learning how to jump-start a diesel truck with two batteries.

Do Trucks Have Two Batteries?jumper cables BK 7825252

It’s not uncommon for diesel trucks to have two batteries. The dual-battery setup cranks extra power that can overcome the higher resistance of a diesel engine. Compression ratios for diesel engines are almost twice those of gasoline engines. It simply takes more oomph to fire up a diesel.

How Do I Jump-Start a Diesel Truck With Two Batteries?

Luckily, you don’t need to find a friendly stranger with a dual-battery vehicle in order to get yours moving again. The batteries in your truck are in parallel. This means you can jump-start your diesel engine by connecting to just one of the batteries — usually the most accessible — in your vehicle’s engine compartment. Once you get the engine started, the alternator will do its job, sending a charge back into both batteries, even at idle.

Here’s how to do it:

  1. Put both vehicles in either “park” (automatic transmission) or “neutral” (manual transmission).
  2. Turn off lights and other accessories in the vehicle you’re jump-starting.
  3. Connect one clamp of the red jumper cables to the positive terminal of the dead battery. The terminal will either have a “+” symbol or a red cover.
  4. Connect the cable’s second clamp to the good battery’s positive terminal.
  5. Connect one of the black cable’s clamps to the good battery’s negative terminal.
  6. Find a piece of unpainted metal on the vehicle you’re jumping (the alternator bracket is a great choice), and connect the last black cable’s clamp to it.
  7. Start the engine of the vehicle with the good battery, and let it run for a few minutes. You’re putting juice back into a dead battery, which will take a moment.
  8. Start cranking the engine on your diesel. It may take a while to fire up, so you might need to give it another few minutes of juice from the good battery.
  9. Once the engine turns over, remove the black cables from both vehicles one at a time, making sure they don’t touch metal, each other or the red cable.
  10. Remove the red cables from both vehicles one at a time. Stay careful and alert until the clamps are detached from any batteries to avoid electric shock or fire.

Remember to let your revived truck run for a bit, allowing the alternator to put power back into both batteries. Take your truck for a drive, and try not to shut off the engine for at least 20 minutes.

Keep those jumper cables handy, just in case. Now that you know how to jump-start a diesel truck with two batteries, you’ll know just what to do when someone else needs your help.

Check out all the battery cables available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on jump-starting your vehicle, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.

Mike Hagerty View All

Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of MikeHagertyCars.com, and contributes car reviews to the Los Altos Town Crier and losaltosonline.com. Previous outlets have included KFBK and KFBK.com in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and BBCCars.com.

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