Why Do Diesel Trucks Have Two Batteries?

Did you know most diesel trucks have two batteries? You might know this fact, but do you know why? Keep reading to find out why it is important to know about your batteries to keep your diesel truck running at its optimum performance level.

Can a diesel truck run on one battery?

Diesel truck batteries in a row
Diesel trucks require two batteries to power the truck properly | Yegor AleyevTASS via Getty Images

In general, your diesel truck needs two batteries because it requires more power to do things. It has a bigger motor that requires more power to turn over. You might be able to get away with one battery, but it is not suggested.

Diesel Pickup Pros has some good information about the batteries in question. Diesel engines need to crank at a higher amp because the trucks demand a high-resistance load to turn over.

Parallel batteries vs. series batteries

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There are two types of battery layouts for these trucks: parallel batteries or series batteries. Most of the trucks on the market use the parallel-joined battery setup. This uses a 12-volt system that connects both positive and negative terminals.

If that sounds confusing, picture it like a criss-cross situation. The negative terminal on one battery is connected to the negative terminal on the other. The positive is connected to the positive. This allows the batteries to double up on amps, but not the voltage, according to Battery Stuff.

The benefit of a parallel battery setup is that the energy current will remain consistent. It will not surge and mess with the other components on your truck.

One drawback to this is that you need a heavy-duty cable to avoid burnout. These can be more expensive to replace should you need a replacement.

Series batteries are almost an antiquated setup at this point. When batteries are connected in a series setup, the voltage of both is added up. The amps remain the same, but the voltage increases. This is no longer in practice as much because parallel batteries offer a more reliable setup.

These would be connected more linearly and are good when you need a higher voltage, but it is not a practice most trucks use anymore. If a battery is installed incorrectly, it can fry your electrical system pretty quickly.

Do you change both batteries at once?

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Depending on where you live, the weather can impact the life of your batteries. If you live in extremely hot or cold climates, it might make your battery life shorter than anticipated. Additionally, corrosion will not have a positive impact on your battery life.

If one battery starts to give you trouble, you should go ahead and replace both batteries at once. You want the batteries to be fairly identical in battery life to ensure your truck runs at the optimum level.

If you install batteries at different times, the batteries might act differently. One might be overcharged while the other is undercharged. This can make the battery life on both shorter.

It is recommended that you check your batteries occasionally to ensure there is no corrosion. This will also help extend battery life. Overall, batteries for diesel trucks have a life expectancy of four years. Extreme temperatures (both hot and cold), might impact life expectancy.