Diesel trucks are hard on batteries. High compression means high cranking demand, and glow plugs or a grid heater add to the load in cold weather. Most diesel pickups use two batteries for this reason. This guide covers typical replacement timing and how to choose replacements. Refer to your owner's manual for the correct group size and rating for your truck.
Why two batteries
- High cranking demand: diesels need far more current to crank than a gas engine, and two batteries share that load.
- Cold-start aids: glow plugs (Power Stroke, Duramax) or a grid heater (Cummins) draw heavy current before and during starting.
- Reserve capacity: two batteries provide a buffer for accessories and long cranking.
When to replace
- Typical life: often around 4 to 6 years, shorter in extreme heat.
- By symptom: slow cranking, needing a jump, or a battery light are signs to test both batteries.
- Test, do not guess: a load test or conductance test tells you the real state of health.
Replace in pairs
This is the single most important habit for diesel batteries.
- Match them: a new battery paired with a weak old one gets dragged down, so replace both together with a matched pair.
- Same type and rating: use the same chemistry and rating for both so they age evenly.
- Check the cables: corroded or loose cables mimic a bad battery, so clean and tighten connections.
What rating to look for
- Cold cranking amps (CCA): meet or exceed the factory rating, especially in cold climates.
- Group size: match the physical size and terminal layout for your truck; refer to your manual.
- Reserve capacity: higher reserve helps with accessories and extended cranking.
If you need help identifying the correct group size or related electrical parts for your diesel, email sales@coredieselparts.com with your VIN.
Frequently asked questions
Do I have to replace both batteries at once?
It is strongly recommended. A new battery paired with a weak one is pulled down to the weaker battery's level, shortening the life of both. Replace them as a matched pair.
How long do diesel truck batteries last?
Often 4 to 6 years, less in very hot climates. Have both tested once they reach that age or if you notice slow cranking, so you can replace them before they leave you stranded.
What CCA rating do I need?
Meet or exceed the factory cold cranking amp rating, and match the group size for your truck. In cold climates, erring toward higher CCA helps with those demanding winter starts.
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