2018 GMC Sierra 2500HD Battery Size & Group

Quick Answer

• BCI Group Size: Group 31 (Diesel), Group 48/H6 (Gasoline)
• CCA Rating: 900-1000 CCA (Diesel), 730 CCA (Gasoline)
• Reserve Capacity: 180-200 minutes (Diesel), 120-130 minutes (Gasoline)
• AGM vs. Flooded: Most diesel 2500HDs come with AGM from the factory; always recommended to replace with AGM. Gasoline models typically use flooded, but AGM is a beneficial upgrade.
• Terminal Layout: Top post
• Physical Dimensions (Approximate for Group 31): 13" L x 6.8" W x 9.4" H
• Dual-Battery Setup: Yes, diesel models utilize a dual-battery setup.

Replacement Battery Options

For Diesel Models (Group 31 AGM):

• Interstate: MTZ-31 (AGM)
• Optima: Optima D31A (YellowTop AGM)
• DieHard: Platinum AGM Group 31
• Odyssey: ODP-AGM31 (Extreme Series AGM)

For Gasoline Models (Group 48/H6):

• Interstate: MTP-48/H6 (Flooded), MTZ-48/H6 (AGM)
• DieHard: Gold Group 48/H6 (Flooded), Platinum AGM Group 48/H6
• ACDelco: 48AGM professional (AGM)

AGM vs. Flooded — Which Does This Vehicle Need?

For the 2018 GMC Sierra 2500HD, the choice between AGM (Absorbent Glass Mat) and flooded batteries largely depends on the engine type and original equipment.

Diesel models almost exclusively came equipped with AGM batteries from the factory. This is critical for several reasons. Diesel engines, especially in heavy-duty trucks like the Sierra 2500HD, require immense cranking power to start, particularly in cold weather. AGM batteries excel in delivering high CCA (Cold Cranking Amps) and maintaining stable voltage under heavy loads. They are also more resistant to vibration and can handle deeper discharge cycles better than traditional flooded batteries, which is beneficial given the demands placed on a heavy-duty diesel truck's electrical system. If your diesel Sierra came with AGM, it is strongly recommended to replace it with another AGM battery to ensure proper system function and longevity.

Gasoline models typically come with conventional flooded lead-acid batteries. While a quality flooded battery will serve its purpose, an upgrade to an AGM battery for a gasoline 2500HD is a smart move. AGM batteries offer enhanced durability, better performance in extreme temperatures, and a longer lifespan. They are also spill-proof and maintenance-free, offering peace of mind. While not strictly "needed" for gasoline models in the same way they are for diesels, AGM batteries represent a significant upgrade in performance and reliability.

Post-Installation Relearn / Reset Procedure

After replacing the battery in your 2018 GMC Sierra 2500HD, there are a few steps you might need to take to ensure all systems are functioning correctly. The truck's computer (ECM/BCM) monitors battery condition, and a new battery can sometimes trigger diagnostic trouble codes or cause initial quirks if not properly recognized.

1. Idle Relearn: After connecting the new battery, start the engine and let it idle for at least 5-10 minutes without touching the accelerator. This allows the engine control module (ECM) to relearn its idle parameters. You might notice slightly rough or fluctuating idle initially; this is normal.
2. Window Express Up/Down Reset (if applicable): If your power windows lose their one-touch up/down function, roll each window down completely and hold the button for a few seconds. Then, roll each window up completely and hold the button for a few seconds. This usually recalibrates the express function.
3. Radio Presets and Clock: These will likely be lost and need to be reprogrammed.
4. Steering Angle Sensor (if symptoms occur): In rare cases, you might get a "Service StabiliTrak" message. To reset the steering angle sensor, start the engine, turn the steering wheel all the way to the left, then all the way to the right, and then back to the center. Drive the vehicle straight for a short distance (e.g., 100 feet). This should clear the message.
5. Battery Monitoring System (BMS) Reset (Optional but Recommended): Some advanced diagnostic scan tools can perform a specific battery monitoring system (BMS) reset, which tells the vehicle