2018 Ram 2500 Battery Size & Specs: An ASE Mechanic's Guide

As an ASE-certified master technician, I’ve worked on countless heavy-duty trucks, and the 2018 Ram 2500 is a frequent visitor to the bay—usually for routine maintenance like battery replacements. Whether your truck is equipped with the 5.7L HEMI, the 6.4L HEMI, or the mighty 6.7L Cummins Turbo Diesel, having the correct battery setup is essential for reliable starting and handling heavy accessory loads.

Here is your comprehensive guide to the battery requirements, sizes, and specs for the 2018 Ram 2500.

Quick answer

• BCI Group Size: Group H7 (also known as 94R).
• Cold Cranking Amps (CCA): 730 CCA minimum; 800+ CCA is highly recommended, especially for diesel models and cold climates.
• Reserve Capacity (RC): 130 to 140 minutes minimum.
• AGM vs Flooded: Absorbent Glass Mat (AGM) is strongly recommended for longevity and vibration resistance, though standard flooded batteries will work in gas models.
• Terminal Layout: Top Post (Standard SAE), Right Positive.
• Physical Dimensions (H7/94R): Approximately 12.4 inches (Length) x 6.9 inches (Width) x 7.5 inches (Height).
• Dual-Battery Setup (Diesel Only): Models equipped with the 6.7L Cummins Turbo Diesel require two Group H7 (94R) batteries wired in parallel to power the intake air heater and provide the massive cranking power needed for high compression. Always replace both batteries at the same time.

Replacement battery options

When replacing the battery (or batteries) in your 2018 Ram 2500, quality matters. Here are some of the most reliable and popular replacement options on the market:

• Interstate Batteries: MTX-94R/H7 (Premium AGM offering excellent CCA and warranty).
• DieHard: Platinum AGM Battery, Group Size H7/94R (Part number varies by retailer, highly rated for extreme weather).
• Optima: YellowTop DH7 (A premium deep-cycle and starting AGM hybrid, excellent for trucks with winches or aftermarket lighting).
• Odyssey: Performance Series ODP-AGM94R H7 L4 (Known for extreme durability and massive reserve capacity).
• ACDelco: Gold 94RAGM (A solid, OEM-quality AGM replacement option).

AGM vs flooded — which does this vehicle need?

While the gas-powered 2018 Ram 2500s can technically get by with a standard flooded lead-acid battery, I always recommend upgrading to an AGM (Absorbent Glass Mat) battery. For the 6.7L Cummins, AGM is essentially a requirement.

Heavy-duty trucks experience significant chassis vibration, which can shake the active material off the plates of a standard flooded battery. AGM batteries are sealed and heavily compressed, making them exceptionally resistant to vibration. Furthermore, they handle deep discharges better and provide stronger, more consistent cold cranking amps—vital for starting a big V8 or heavy inline-six diesel on a freezing morning.

Post-installation relearn / reset procedure

The 2018 Ram 2500 is equipped with an Intelligent Battery Sensor (IBS) on the negative terminal, which monitors battery state of charge, temperature, and age.

When you install a new battery, the IBS needs to learn the new battery's parameters.

1. Install the new battery (or batteries) and ensure all connections are tight.
2. The vehicle's computer will automatically initiate a relearn over the next few drive cycles.
3. To speed up the process or clear a stubborn "Battery Saver Mode" message, you can use a high-end bi-directional scan tool to manually reset the BMS (Battery Management System).
4. Note: After a battery disconnect, you may also need to reset your radio presets, clock, and one-touch automatic power windows by rolling them all the way down and holding the switch for 2 seconds, then all the way up and holding for 2 seconds.

Signs of a failing battery

Don't wait until you're stranded at a job site. Look out for these warning signs:

• Slow or sluggish engine crank: The most obvious sign, especially notable on the diesel engines.
• "Battery Saver Mode" message: This pop-up on the dashboard indicates the IBS has detected low voltage and is shutting down non-essential electronics.
• Dimming headlights or interior lights: Especially noticeable when coming to a stop or at idle.
• Clicking sound when turning the key: A sign that the starter relay is engaging but there isn't enough amperage to turn the starter motor.
• Swelling or leaking case: If the battery casing looks bloated, replace it immediately.

Common battery issues for this generation

For the 2018 Ram 2500 generation, the most common battery issue usually involves the dual-battery setup on the Cummins diesel. Owners sometimes try to save money by replacing only the battery that tests "bad." Because they are wired in parallel, the older, weaker battery will constantly drain the new battery, killing both prematurely. Always replace diesel batteries in matched pairs.

Another common issue is corrosion building up on the cross-over cable connections (on diesel models) or the main terminals. Because the IBS sensor sits directly on the negative terminal clamp, excess corrosion can cause the sensor to read inaccurately, leading to charging system faults.

Find a trusted shop on Repairius.