2020 Ram 3500 Battery Size, CCA & Group: Complete Replacement Guide

As an ASE-certified master technician, I know firsthand that a heavy-duty truck demands a heavy-duty power source. The 2020 Ram 3500, whether equipped with the 6.4L HEMI V8 or the legendary 6.7L Cummins Turbo Diesel, requires massive cranking power to fire up, especially in cold weather. Choosing the correct battery size, type, and capacity is critical to keeping this workhorse on the road and avoiding unexpected no-start situations.

Here is everything you need to know about the battery specifications, replacement options, and installation procedures for your 2020 Ram 3500.

Quick answer: 2020 Ram 3500 Battery Specifications

• BCI Group Size: Group H7 (also known as 94R).
• Dual-Battery Setup (Diesel): 6.7L Cummins models require two Group H7/94R batteries wired in parallel. The 6.4L HEMI requires a single Group H7/94R.
• Cold Cranking Amps (CCA): Minimum 730 CCA for the 6.4L HEMI. The 6.7L Cummins requires at least 730-800 CCA per battery (1,460–1,600 CCA total).
• Reserve Capacity (RC): 130–140 minutes minimum.
• AGM vs Flooded Requirement: Absorbed Glass Mat (AGM) is highly recommended and often standard from the factory due to the vehicle's electrical demands and Intelligent Battery Sensor (IBS) programming.
• Terminal Layout: Standard top post, Right Positive (Standard polarity).
• Physical Dimensions (H7/94R): Approximately 12.4" Length x 6.9" Width x 7.5" Height.

Replacement battery options

When it comes to replacing the batteries in a 2020 Ram 3500, it is vital to stick to premium brands, especially if you are running the Cummins diesel. (Note: If you have a diesel, always replace both batteries at the same time to prevent the older battery from draining the new one).

Here are some of the most reliable H7/94R replacement options:

• DieHard Platinum AGM (Part # H7-AGM): An excellent choice offering around 850 CCA. Known for exceptional vibration resistance and durability.
• Odyssey Performance Series (Part # ODP-AGM94R H7 L4): Delivers massive starting power and deep cycling capabilities. A top-tier choice for heavily accessorized work trucks.
• Interstate MTX (Part # MTX-94R H7): A premium AGM battery offering 850 CCA and long-lasting reliability.
• Optima YellowTop (Part # DH7): Offers excellent deep-cycle and cranking power, ideal for trucks running winches, inverters, or heavy trailer electrical loads.
• ACDelco Gold AGM (Part # 94RAGM): An OEM-quality alternative that perfectly matches the factory specifications for reliable everyday use.

AGM vs flooded — which does this vehicle need?

While older generations of trucks ran perfectly fine on traditional flooded lead-acid batteries, the 2020 Ram 3500 relies heavily on an AGM (Absorbed Glass Mat) battery.

Modern Rams feature a highly complex electrical system, complete with advanced infotainment systems, multiple control modules, and an Intelligent Battery Sensor (IBS). AGM batteries charge up to five times faster, withstand deep discharges better, and are far more resistant to the intense vibrations produced by heavy-duty towing and the rumble of the Cummins diesel engine. If your truck came with an AGM battery from the factory (which most 2020 models do), you must replace it with an AGM to prevent premature failure and charging system malfunctions.

Post-installation relearn / reset procedure

The 2020 Ram 3500 is equipped with an Intelligent Battery Sensor (IBS) attached to the negative battery terminal. The IBS monitors battery state of charge and health, adjusting the alternator output accordingly.

When you replace the battery (or batteries), the system needs to recognize the new state of charge:

1. Ensure the ignition is fully off and all doors are closed.
2. Disconnect the negative terminals first, then the positive.
3. Install the new batteries, connecting positive first, then negative.
4. The Relearn: In most cases, the IBS will automatically recalibrate if the truck is left locked and undisturbed for 4 to 8 hours (an overnight sit is perfect).
5. Alternatively, an ASE-certified technician can use an advanced bi-directional scan tool to manually perform an IBS reset in the Body Control Module (BCM).

Signs of a failing battery

Heavy-duty batteries often give warning signs before they completely fail. Watch out for:

• Slow or labored engine cranking: Especially noticeable on the Cummins diesel, which requires massive torque to turn over.
• "Battery Saver Mode" messages: The dashboard may display messages indicating that auxiliary systems are being shut down to preserve starting power.
• Dimming headlights or interior lights: Especially when idling or when the intake heater grid cycles on a cold diesel engine.
• Corrosion build-up: Excessive white/blue powder around the top posts.

Common battery issues for this generation

For the 2019+ (5th Generation) HD Rams, the most common battery issue revolves around the diesel intake grid heater. On cold mornings, the grid heater draws a massive amount of amperage, significantly taxing the batteries. If one battery in the dual-battery setup develops a weak cell, it will constantly drain the healthy battery, leading to premature failure of the alternator and both batteries.

Additionally, parasitic draws from aftermarket accessories (like dash cams, light bars, or trailer brake controllers) can slowly degrade the batteries if they aren't properly isolated.

Replacing heavy-duty truck batteries can be a literal heavy lift. If you want to ensure the job is done right, the electrical connections are properly cleaned, and the IBS is accurately reset, let a professional handle it. Find a trusted shop on Repairius.