2020 Subaru Forester Battery Replacement Guide

Quick answer

• BCI Group Size: 25 or 35
• CCA Rating: 550-640 CCA (minimum)
• Reserve Capacity: 90-110 minutes (minimum)
• AGM vs. Flooded: Flooded (standard) Wet Cell, but AGM is a popular upgrade
• Terminal Layout: Top post, typically positive on the right (SAE)
• Physical Dimensions: Varies slightly by group size, but generally similar for 25/35.
• Dual-Battery Setup: Not applicable (not a diesel vehicle)

Replacement battery options

• Interstate: MT-25 (Group 25), MT-35 (Group 35)
• Optima: YellowTop DH6 (H6 group, may require tray modification), RedTop 35 (Group 35)
• DieHard: Gold 25 (Group 25), Gold 35 (Group 35)
• Odyssey: 35-PC1400 (Group 35)
• ACDelco: 25AGM (Group 25 AGM), 35AGM (Group 35 AGM)

AGM vs flooded — which does this vehicle need?

The 2020 Subaru Forester originally came equipped with a standard flooded (wet cell) lead-acid battery. This type of battery is perfectly adequate for the vehicle's needs and is generally the most cost-effective option. It requires occasional maintenance, such as checking and topping off electrolyte levels, though many modern flooded batteries are "maintenance-free" in that they are sealed and don't require regular topping off.

However, upgrading to an Absorbed Glass Mat (AGM) battery is a popular choice for many Forester owners and offers several advantages. AGM batteries are sealed, leak-proof, and maintenance-free. They are also more resistant to vibration, have a lower self-discharge rate, and often provide better performance in extreme temperatures. For vehicles with start-stop technology, or those with many electronic accessories, an AGM battery can handle the increased electrical demands more effectively. While not strictly "needed," an AGM battery can offer enhanced reliability and longevity for your 2020 Forester.

Post-installation relearn / reset procedure

After replacing the battery in your 2020 Subaru Forester, it's important to be aware of a few potential issues and a simple procedure to help your vehicle "relearn" some of its settings:

1. Idle Relearn: The engine control unit (ECU) may need to re-learn its idle parameters. After connecting the new battery, start the engine and let it idle for 10-15 minutes without touching the accelerator. This allows the ECU to recalibrate. You might notice slightly rough or fluctuating idle for a short period initially.
2. Window and Sunroof Initialization: Some Subaru models require re-initializing the power windows and sunroof (if equipped) after a battery disconnect. For windows, fully open each window, then fully close it, holding the switch for 2-3 seconds at each extreme. The sunroof procedure typically involves holding the open or close switch for a few seconds until it completes a full cycle.
3. Radio Presets and Clock: These will likely be reset and will need to be reprogrammed manually.
4. Drive Cycle: It may take a few drive cycles for the vehicle's onboard diagnostic (OBD) system to reset all readiness monitors. This is particularly important if you need to pass an emissions inspection soon after battery replacement.

Signs of a failing battery

• Slow Engine Crank: The most common sign. If your engine cranks slowly or struggles to turn over, it's often an indicator that the battery is losing its charge or capacity.
• Dim Headlights/Interior Lights: When the engine is off, if your lights appear dim, the battery may be weak.
• Warning Lights: A battery warning light on your dashboard is a clear indicator of a problem.
• Corrosion on Terminals: White or blue powdery substance on the battery terminals can indicate a poor connection or acid leakage, both of which hinder performance.
• Swelling Battery Case: If the battery case appears swollen or bloated, especially on the sides, it's a sign of internal damage, often due to overcharging or extreme heat.
• Age: Automotive batteries typically last 3-5 years. If your battery is older than this, it's on borrowed time.

Common battery issues for this generation

The 2020 Subaru Forester, like many modern vehicles, has an increasing number of electronic systems that draw power even when the car is off. This can sometimes lead to:

• Parasitic Draws: A component (e.g., infotainment system, remote access modules) can draw power when the vehicle is off, slowly draining the battery over time, especially if the car sits for extended periods.
• Start-Stop Technology Strain: Vehicles with automatic start-stop systems place greater demands on the battery, as it needs to handle frequent engine restarts. While the original battery is designed for this, continuous short trips or extreme temperatures can shorten its life.
• Factory Battery Longevity: Some owners have reported that the original factory-installed batteries in Subarus of this generation had a shorter lifespan than expected. This isn't necessarily a defect, but rather a characteristic of OEM batteries often being chosen for cost-effectiveness rather than maximum longevity.
• Terminal Corrosion: While not unique to the Forester, keeping battery terminals clean and free of corrosion is crucial for reliable starting and charging.

Regular battery testing, especially as your battery approaches the 3-year mark, can help you proactively replace it before you're left stranded.

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