2021 Subaru Outback Battery: Group Size, CCA & Replacement Guide

Quick answer

• BCI Group Size: Group 47 (also referred to as H5 or L2)
• Cold Cranking Amps (CCA): 640 CCA
• Reserve Capacity (RC): Approximately 100 minutes
• Battery Type: Enhanced Flooded Battery (EFB) or Absorbent Glass Mat (AGM) required
• Terminal Layout: Left-hand positive (when viewed from the front)
• Physical Dimensions (approximate): 9.69" L x 6.89" W x 7.48" H (246mm x 175mm x 190mm)

Replacement battery options

• Interstate: MTX-47/H5
• DieHard: Platinum AGM Battery, Group Size H5, 680 CCA (DH-H5)
• ACDelco: Gold 47AGM
• Optima: YELLOWTOP DH5 (part number DS46B24R)
• Odyssey: ODP-AGM47H5L2

AGM vs flooded — which does this vehicle need?

The 2021 Subaru Outback comes equipped with an auto start-stop system. This technology, designed to improve fuel efficiency by shutting the engine off at stops, places a much higher demand on the battery than a traditional starting system. To handle this increased load and the frequent cycling, Subaru uses an Enhanced Flooded Battery (EFB) from the factory.

When it's time for a replacement, you must use either another EFB or, for a performance upgrade, an Absorbent Glass Mat (AGM) battery. A standard flooded lead-acid battery is not sufficient and will have a very short service life in this application. AGM batteries offer superior vibration resistance, deeper cycling capability, and a longer overall lifespan, making them an excellent choice for the 2021 Outback.

Post-installation relearn / reset procedure

After replacing the battery in your 2021 Outback, a reset procedure is necessary to ensure the vehicle's systems, particularly the charging system, recognize the new battery.

1. Window/Moonroof Reset: You may need to reset the auto up/down feature for the windows and moonroof. For each window, press and hold the down switch until the window is fully open, then hold it for another second. Then, pull and hold the up switch until the window is fully closed, and hold for another second. Repeat for the moonroof.
2. Auto Start-Stop System: The auto start-stop system may not function immediately after a battery change. The vehicle's Battery Sensor Module (BSM) needs to relearn the new battery's state of charge. This typically happens on its own after a few drive cycles, which should include some periods of steady cruising.
3. No Special Scan Tool Required: For a simple battery replacement, you generally do not need a special scan tool to "register" the new battery as you might with some European brands. The onboard systems will adapt, but the relearn period is crucial.

Signs of a failing battery

• Slow Engine Crank: The engine turns over sluggishly, especially on cold mornings.
• Auto Start-Stop Malfunctions: The start-stop system ceases to function, often accompanied by a message on the multi-function display.
• Dimming Lights: Headlights and interior lights may dim noticeably when the engine is off or at idle.
• Warning Lights: A battery or charging system warning light may illuminate on the dashboard.
• Electrical Gremlins: Unexplained issues with the radio, infotainment system, or power windows can sometimes be traced back to a weak battery.

Common battery issues for this generation

The most reported battery-related issue for the 2017–2022 Subaru Outback generation is premature battery failure and a perceived "battery drain." Several factors contribute to this: the higher electrical load from modern features, the demands of the auto start-stop system, and the driving habits of the owner. Short, infrequent trips may not be long enough for the alternator to fully recharge the battery, leading to a gradual decline in its state of charge and eventual failure. A class-action lawsuit was even filed regarding these issues, alleging that the battery and charging system were not robust enough for the vehicle's demands. Using a high-quality AGM replacement and ensuring the car is driven for at least 30 minutes regularly can help mitigate these problems.

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