2024 Subaru Forester — Battery Size & Group

Quick answer

• BCI group size: Group 35 (12V)
• Recommended CCA: 620–650+ CCA (AGM); minimum around 550 CCA in mild climates
• Reserve capacity (RC): ~100 minutes (varies by brand, ~95–120 min typical)
• Type: AGM strongly recommended/required for models with Auto Start-Stop (most 2024 Foresters in North America)
• Terminal layout: SAE top‑post; positive on the right when posts are closest (BCI Group 35 orientation)
• Physical dimensions (Group 35): approx. 9.06" L × 6.88" W × 8.86–8.94" H (230 × 175 × 225–227 mm)
• Dual‑battery setup (diesel): Not applicable (Forester is gasoline-only in the U.S./Canada)

Replacement battery options

These are popular, direct‑fit Group 35 choices. Use AGM for Auto Start‑Stop; flooded can fit but isn’t recommended for start‑stop duty.

• Interstate MTX‑35 (AGM) — premium replacement for start‑stop systems
• Interstate MTP‑35 (flooded) — fits, but not ideal if your Forester uses Auto Start‑Stop
• Optima YellowTop D35 (AGM) — deep‑cycle AGM that tolerates frequent cycling from start‑stop
• DieHard Platinum AGM — Group 35 (AGM) — strong CCA and RC, maintenance‑free
• Odyssey 35‑PC1400 (AGM) — high reserve capacity and rugged construction
• ACDelco Gold/Professional AGM — Group 35 (AGM) — OE‑style fit and venting

Tip: If you regularly see freezing temps, choose the higher‑CCA AGM option available in your brand of choice.

AGM vs flooded — which does this vehicle need?

The 2024 Forester’s electrical system and widespread use of Auto Start‑Stop put heavier cycling demands on the battery than older models. AGM (Absorbent Glass Mat) batteries are designed for this duty:

• Better deep‑cycle durability for frequent restarts
• Lower internal resistance for faster recharge on short trips
• Spill‑proof and more vibration‑resistant

For 2024 Forester models with Auto Start‑Stop (typical in North America), use an AGM Group 35. A conventional flooded Group 35 will physically fit and can crank the engine, but it often delivers shorter service life and reduced start‑stop performance. If your market/trim does not use Auto Start‑Stop, an upgraded AGM is still a worthwhile reliability improvement.

Post‑installation relearn / reset procedure

Subaru modules relearn quickly, but following these steps helps avoid idle and start‑stop issues:

1. Memory saver (recommended): Before disconnecting the old battery, connect a 12V memory saver to the OBD‑II port to preserve presets and window calibration.
2. Installation: Install the new Group 35 battery. Tighten terminals to spec; connect negative last. Ensure clean, tight, corrosion‑free posts.
3. Initial start and idle relearn:
   • Start engine; let it idle with all accessories OFF for 10 minutes.
   • Then turn A/C and headlights ON and let it idle another 5–10 minutes. This allows the battery sensor and ECU to adapt to the new state of charge.
4. Drive cycle: Take a 10–15 minute mixed drive (light throttle, some stop‑and‑go). Auto Start‑Stop may be inhibited for the first few trips until the system verifies battery health.
5. Power window initialization: For each door, key ON, hold the switch to fully close the window and continue holding for 2–3 seconds. Then fully open and hold 2–3 seconds. Repeat if one‑touch doesn’t work.
6. Radio/clock/presets: Re‑enter as needed (skipped if you used a memory saver).
7. Steering angle/eyesight note: If the steering warning appears, slowly turn the wheel lock‑to‑lock once while moving at parking‑lot speed to help the steering angle sensor finalize.
8. Liftgate (if equipped): If power tailgate acts erratically, manually open/close once, then use the power switch to open/close once to recalibrate.

Signs of a failing battery

• Slower cranking, especially after short trips or in cold weather
• Auto Start‑Stop “not available” more often, or disabled warnings
• Dim interior lights at idle, flickering infotainment screen
• Clock resets, lost radio presets, or erratic window one‑touch
• Corroded terminals or swollen battery case
• Voltage below ~12.4V after an overnight rest (with no accessories left on)

Common battery issues for this generation

• Short‑trip driving + Start‑Stop cycling: Repeated short hops never fully recharge the battery. An AGM with higher CCA/RC tolerates this better.
• Parasitic draw complaints: Smart keys, telematics (STARLINK), and security modules can contribute to small but continuous draws. Healthy AGM capacity and proper charging mitigate overnight voltage dips.
• Battery sensor sensitivity: The negative‑terminal battery current sensor (IBS) needs clean, tight connections. Poor grounds or corrosion can cause inaccurate state‑of‑charge readings and Start‑Stop disablement.
• Cold‑weather performance: Group 35 is compact; in very cold climates, choose the highest‑CCA AGM available and keep terminals clean to reduce voltage drop.
• Terminal corrosion and loose clamps: Common after a few years; always clean and apply a light protective spray when installing the new battery.

Selecting a quality AGM Group 35 with at least 620–650 CCA and ~100 minutes RC will match or exceed the 2024 Forester’s original performance and improve reliability with Auto Start‑Stop.

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