2017 Subaru Forester Battery Replacement Guide

Quick Answer

• BCI Group Size: 25 or 35
• CCA Rating: 550-650 CCA (varies by model and engine)
• Reserve Capacity: 90-110 RC
• AGM vs. Flooded: Either is suitable, but AGM is recommended for enhanced performance and longevity.
• Terminal Layout: Top post, typically positive on the right.
• Physical Dimensions: (Group 25) 9.06" L x 6.81" W x 8.88" H; (Group 35) 9.06" L x 6.81" W x 8.88" H
• Dual-Battery Setup: Not applicable (not a diesel model).

Replacement Battery Options

• Interstate: MT5-25 (Group 25), MT5-35 (Group 35)
• Optima: 8020-164 35 RedTop (Group 35)
• DieHard: Platinum AGM Group 35
• Odyssey: 35-PC1400 (Group 35)
• ACDelco: 35AGM (Group 35)

AGM vs Flooded — Which Does This Vehicle Need?

For your 2017 Subaru Forester, both AGM (Absorbent Glass Mat) and traditional flooded lead-acid batteries are suitable. However, an AGM battery is generally recommended for several reasons:

• Durability: AGM batteries are more resistant to vibrations and impacts, which can be beneficial for a vehicle like the Forester that might encounter varied road conditions.
• Performance: They offer more consistent power delivery and better performance in extreme temperatures.
• Longevity: While typically more expensive upfront, AGM batteries often last longer than flooded batteries, offering better long-term value.
• Maintenance-Free: AGM batteries are sealed and do not require watering, making them maintenance-free.

Flooded batteries are a more economical choice and will also work perfectly fine, provided they meet the BCI group size and CCA requirements. If you primarily do short drives or live in a mild climate, a quality flooded battery will serve you well. However, if you're looking for maximum reliability, especially in cold weather, an AGM is the superior choice.

Post-Installation Relearn / Reset Procedure

After replacing the battery in your 2017 Subaru Forester, it's important to be aware of potential issues and a simple reset procedure. Modern vehicles rely heavily on their electrical systems, and a battery disconnect can sometimes lead to minor quirks.

1. Idle Relearn: The engine control module (ECM) may need to re-learn its idle parameters. After connecting the new battery, start the vehicle and let it idle for about 10-15 minutes without touching the accelerator. This allows the ECM to adjust to the new power source and re-establish proper idle. You might notice slightly rough idling initially, but it should smooth out.
2. Window One-Touch Function: The automatic up/down function for your power windows might need to be reset. To do this, lower each window completely, then raise it completely, holding the button for an additional 2-3 seconds at the top and bottom of each cycle. Repeat for all windows.
3. Radio Presets: Your radio presets will likely be lost. You will need to reprogram your favorite stations.
4. Clock: The clock will need to be reset to the correct time.
5. Steering Angle Sensor (less common but possible): In some cases, the Vehicle Dynamics Control (VDC) system might illuminate a warning light. To reset this, drive the vehicle straight at a low speed (around 10-15 mph) for a short distance. This often allows the system to recalibrate the steering angle sensor.

If any persistent warning lights appear after the battery replacement, consult your owner's manual or a qualified mechanic.

Signs of a Failing Battery

Recognizing the signs of a dying battery can prevent you from being stranded. Look out for these common indicators:

• Slow Engine Crank: The most common sign. If your engine cranks slowly, struggles to turn over, or sounds weak when you try to start it, your battery is likely on its way out.
• Dashboard Warning Lights: A battery warning light on your dashboard is a clear indicator of a charging system problem, which often points back to the battery.
• Dim Headlights and Interior Lights: If your lights appear dim, especially when the engine is off, it suggests a weak battery.
• Electronic Issues: Malfunctioning power windows, radio, or other electrical accessories can be a symptom of an insufficient power supply.
• Corrosion on Battery Terminals: White or bluish powdery corrosion around the battery terminals can indicate a poor connection or a leaking battery, both of which reduce its efficiency.
• Swollen or Bulging Battery Case: This is a serious sign of internal battery damage, often caused by overcharging, and requires immediate replacement.
• Old Age: Car batteries typically last 3-5 years. If your battery is older than this, it's a good idea to have it tested regularly.

Common Battery Issues for This Generation

While the 2017 Subaru Forester is generally reliable, some common battery-related issues can arise:

• Parasitic Draws: Even when the vehicle is off, certain electrical components can draw a small amount of power, known as a parasitic draw. Over time, especially if the car sits for extended periods, this can drain the battery. Common culprits can include aftermarket accessories, malfunctioning internal lights, or even a faulty multimedia system.
• Cold Weather Performance: Like all batteries, the Forester's battery can experience reduced capacity and performance in extremely cold temperatures, making starting more difficult. Ensuring your battery has sufficient CCA for your climate is crucial.
• Short Trips: Frequent short drives, where the engine doesn't run long enough to fully recharge the battery, can lead to premature battery degradation.
• OEM Battery Lifespan: While some OEM batteries can last a while, others might only last 3-4 years. Being proactive about battery testing as your car ages is a good practice.

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