How Long Should a Diesel Battery Last?

OPTIMA Batteries
Milwaukee, WI
We were approached at the SEMA Show by an Ultra4 racer, who ran two of our batteries in his buggy at King of the Hammers and he indicated he was having trouble with them. His rig wasn't diesel-powered, so why is this relevant to diesel truck owners and how long their batteries last? Because both applications involve vehicles that use multiple batteries. In this case, two OPTIMA D34/78 YELLOWTOP batteries. The Ultra4 racer indicated the two batteries were a "matched set" that he bought at the same time, but as the photo above shows, that is clearly not the case, at least with the labels.
Upon closer inspection, one battery had a build date of August 2, 2008, while the other battery had a build date of August 8, 2018. While the two batteries were identical in the type of battery (SPIRALCELL AGM) and size of battery (D34/78 YELLOWTOPs), they couldn't be much further apart on age. Whenever someone has a vehicle, whether it is an Ultra4 or diesel truck, that runs two or more batteries, the batteries in that application need to be identical in the type, size and especially the AGE of the battery. Why is age so important?
As batteries age, their ability to accept and deliver current changes. Internal resistance slowly increases and capacity slowly decreases. As a result, an older battery may not charge up at the same rate as a newer battery that is identical in every other way and it may not deliver current at the same rate. In essence, you are running two different batteries. Doing that can shorten the lifespan of both batteries, as one battery may be constantly overcharged, while the other battery is constantly undercharged, regardless of whether they are wired together in series or parallel. The same thing can happen if you run a flooded battery (higher internal resistance) with an AGM battery (lower internal resistance) or a physically larger battery (more reserve capacity) with a smaller battery (less reserve capacity).
So if you have a diesel truck that runs two or three batteries and one needs to be replaced, every other battery in that application needs to be replaced as well. That doesn't mean you need to recycle the other battery if it still works, but you may need to move it to another vehicle or application, that only uses one battery. But does that answer the question of how long a diesel truck battery should last?
While it helps explain how to maximize battery performance and lifespan, it doesn't provide a definitive answer, because one single answer doesn't exist. Some batteries could last a few months in extreme applications, while others could last 20 years or more. Batteries used in extreme temperatures (both hot & cold) don't last as long as batteries used in more moderate climates. Batteries that have their voltage properly-maintained tend to last longer than batteries that are often discharged and left sitting in that state for extended periods of time. Batteries that routinely see very shallow discharge cycles will have more cycle life, than batteries that routinely see deep discharge cycles.
The result is the question of how long a diesel truck battery should last really turns into an answer of how much are you willing to do to maximize the performance and lifespan of your diesel truck battery? The first step is starting with batteries that are identical in age, size and type. OPTIMA Batteries can last up to three times as long as a traditional flooded lead-acid battery in the same application, so that's a good start too, but AGM batteries in general should last longer than their flooded counterparts. Protect your battery from extreme temperatures, both hot & cold and make sure your battery (or batteries) are big enough for your application. Finally, keep your batteries fully-charged to at least 12.6 volts (at least 13.0 volts for our YELLOWTOP batteries) whenever possible to maximize the performance and lifespan of your batteries.
If you think one or more of your batteries might need replacing, fully-charge them and have them load-tested (most battery professionals offer this service for free and you can find one near you here). One thing to remember, if you are running D31T YELLOWTOP batteries or any other batteries with threaded terminals, those threaded posts are used to secure the cable connection to the base of the battery, not to transmit current. Watch this video to see how to properly load test a battery with threaded terminals: