The battery size depends on the engine: diesel models typically use two 12-volt Group 31 batteries, while gasoline versions usually use a single 12-volt battery (commonly Group 65), with some trims using Group 75 depending on equipment. Verify your specific vehicle to be sure.
Engine-specific battery setup
Below is a general guide to the common configurations found in the 2008 Sierra 2500HD. Vehicle variations by trim, production date, and regional specs can change the exact setup.
- Duramax diesel (6.6L): dual 12-volt batteries, typically Group 31, wired in parallel to supply higher starting power and electrical support for diesel systems.
- Gasoline 6.0L V8: usually a single 12-volt battery, commonly Group 65; some configurations may use Group 75 depending on option packages or climate equipment.
Conclusion: The diesel version almost always has a dual-battery arrangement with Group 31 batteries; the gasoline version more often uses a single larger battery, but exceptions exist based on trim and options. Always verify on the actual vehicle.
How to verify the correct size on your truck
Use these steps to confirm the precise battery size for your specific Sierra 2500HD.
- Inspect the battery label for the Group Size code (for example, 31, 65, or 75) printed on the top or side of each battery.
- Check the owner's manual or the under-hood placard for the recommended battery size and the cold-cranking amps (CCA) rating for your engine and trim.
- If needed, consult the GM parts catalog or a GMC dealership service department using your VIN to confirm the exact OEM specification.
Conclusion: Confirming the exact group size and CCA ensures you replace with the correct battery configuration for reliable starting and electrical performance.
Summary
The 2008 GMC Sierra 2500HD typically uses two Group 31 batteries on the diesel version and a single Group 65 battery on most gasoline versions, with some trims potentially using Group 75. Due to variations by trim and options, always verify the correct size by checking the battery itself, the owner's manual, or a GMC dealer.