Diesel Automotive Starting Battery Replacement

Ram 3500 Alternator Battery Check - Truck Camper Adventure

Any discussion of batteries on this website usually relates to the deep cycle batteries found in your truck camper. However, the batteries found underneath the hood of your truck are just as important. Without a reliable pair of starting batteries, your rig wouldn’t be able to go anywhere or do anything. This short article provides basic information about automotive starting batteries, how to troubleshoot them, how to replace them, and the best places to buy them when they’re needed.

A few weeks ago I replaced the 12 volt batteries in my 2013 Ram 3500 pickup truck. It’s never fun having to fork out big bucks for automotive starting batteries. What makes the sticker shock even worse is that diesel engines require two rather than one. Automotive starting batteries typically last about five years, but the triple-digit heat here in Arizona reduces their life expectancy to three to four years at the most (mine lasted a little over three years). What was the first sign of trouble? When our truck failed to start on a recent 70 degree morning in Las Vegas. The truck ran great after getting a jump-start. This usually indicates that the alternator is working, but it’s always a good idea to take a few voltage readings with the engine running to make sure the alternator is putting out the correct amount of voltage. If you get a reading higher than 14 volts with your engine running (mine read 14.22 volts) then you know your alternator is working fine and is producing a sufficient amount of voltage to charge your batteries.

What’s the best way of diagnosing a battery problem? By taking separate voltage readings of each using a multi-meter or battery analyzer after removing them from your truck. Yeah, I know doing this is a pain, but it’s important to do this in diesels because removing them electrically separates the batteries from each other. Diesel starting batteries, like most 12 volt RV battery systems, are wired in parallel, so any readings you take with the batteries still connected to the truck are misleading, you’ll get the same readings on each battery. Anyhow, the voltage readings I got on my work bench at home were very interesting, though not surprising. The driver side battery read 12.5 volts, which is okay, but the passenger side battery read only 11.1 volts, which is obviously bad, especially in light of the fact that this reading was taken just a few hours after a full charge.

While getting accurate voltage readings of your batteries important, it’s important to check the cold cranking amps (CCA) and internal resistance of your batteries as well. You’ll need a good digital battery analyzer, like the one made by Cen-Tech, to get these readings. The CCA check is self-explanatory. It tells you how many CCAs the battery provides. This reading is important because the number of amps is what will start your truck or not. The batteries in my truck are rated for 730 CCA. A good battery will always generate the rated amount of amperage or more. The internal resistance check also provides important information on the health of your battery. The lower the resistance the better. A good resistance reading will be around 3 to 4 milliohms. A much higher reading of, say, 20 milliohms means the lead plates in your battery are corroded and degraded and are not conducting very well. When this happens it’s time to replace the battery.

Cen-tech Digital Battery Analyzer - Truck Camper Adventure
Display readings of a Cen-tech digital battery analyzer.

Even though only one of my starting batteries was bad, I needed to replace both. Why? Because you never want to pair up an old battery with a new one. When one battery goes bad, it draws down the good one. When you pair up batteries in your rig you always want them to be the same size and age. The good battery was nearing the end of its life anyhow and we didn’t want to take the risk of using it and having it fail in the middle of one of our outings. We were able to use USAA roadside assistance to get a jump in Las Vegas when this battery failed, but we won’t always be able to rely upon this service in the more remote places where we like to visit. What batteries did I end of buying as replacements? I decided to try out a pair of Deka Gold maintenance free batteries. These aren’t AGMs, but a sealed wet cell type of battery. They are rated for 790 CCA and have a two-year warranty. We’ll see how they perform in Arizona’s heat.

Costco Batteries - Truck Camper Adventure
Battery display at Costco.

Where are the best places to buy new automotive starting batteries? Places that sell batteries in high volume like Walmart, Sam’s Club, and Costco. When you buy from these heavy weight sellers you’ll be sure to get fresh batteries. Not only that, but the prices and warranties that they offer are the best, especially Costco’s. The only problem going this route is the limited selection that they offer. Unfortunately, only the most common and popular sizes are sold. None of these places sold the size 30 battery I needed for my truck. That’s why I had to buy my batteries from a specialty outlet here in town. Going this route means you’ll pay a bit more, but they offer a better selection than the big three.

One term you might not be familiar with is cold cranking amps. This rating isn’t typically associated with true deep cycle batteries, just automotive starting batteries. The rating refers to the amount of current a given battery can deliver for 30 seconds at 0 degrees F without dropping below 7.2 volts. The value of CCA changes with battery temperature. As the temperature goes down, the energy capability of the battery is reduced. For example, at 80 degrees a battery will provide 100 percent of its rated capacity, at 0 degrees that falls to 40 percent.

Deka Automotive Starting Battery - Truck Camper Adventure
A brand new Deka Gold 12 volt automotive starting battery.

One more thing. Some of you may be wondering why two batteries are needed to start a diesel engine. There are two reasons. The main reason is that it takes a lot of amperage to turnover a high-compression diesel engine. The other has to do with the heater grid or glow plugs which require a large amount of current at startup (Cummins diesels are equipped with a heater grid not glow plugs). As was stated earlier, the starting batteries found in diesel trucks are wired in parallel. Neither battery has a specific duty. When batteries are wired in parallel you double the CCA rating. This is a lot of juice and most diesel trucks today need it. Some older diesels can start with just one battery, but the newer diesel trucks require two, like my 2013 Ram 3500.

About Mello Mike 878 Articles
Mello Mike is an Arizona native, author, and the founder of Truck Camper Adventure. He's been RV'ing since 2002, is a certified RVIA Level 1 RV Technician, and has restored several Airstream travel trailers. A communications expert and licensed ham radio operator (KK7TCA), he retired from the U.S. Navy in 2004 as a CWO3 after 24 years, holds a BS degree, and now runs Truck Camper Adventure full-time. He also does some RV consulting, repairs, and inspections on the side. He currently rolls in a 4WD Ram 3500 outfitted with a SherpTek truck bed with a Bundutec Roadrunner mounted on top.

1 Comment

  1. To explain just a little more about the diesel cranking, the older trucks with a mechanical injection pump would get full fuel pressure on every compression stroke since the pump has a cam that lifts the plunger to charge the injector. The newer truck Diesels have a high pressure common rail fuel system, the rail is like a manifold, pressure must be built up in the rail before the injectors can fire the atomized spray. That requires cranking the engine enough for the pump to buils up the rail pressure.

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