2020 Subaru Forester Battery Drain Problem Diagnosis

Few things are more frustrating than walking out to your 2020 Subaru Forester only to find it won't start due to a dead battery. Even worse is when this happens repeatedly, suggesting a deeper issue than just an old battery. If you're constantly jump-starting your Forester or replacing batteries frequently, you're likely dealing with a parasitic draw – an electrical component or system that continues to consume power even when the vehicle is turned off.

What drivers notice on this 2020 Subaru Forester

Drivers of the 2020 Subaru Forester experiencing a battery drain problem often report a range of symptoms, from minor annoyances to complete vehicle immobilization. The most obvious sign is a completely dead battery after the car has been parked for a few hours or overnight. However, more subtle indications can appear before a full failure.

• Repeatedly dead battery: The most common and frustrating symptom, requiring frequent jump-starts or battery replacements.
• Slow or weak cranking: The engine struggles to turn over, especially after the vehicle has sat for a while.
• Interior lights staying on: Dome lights, glove box lights, or trunk lights may not turn off completely.
• Warning lights: Dashboard warning lights (e.g., battery light, check engine light) may illuminate, sometimes intermittently.
• Unusual electrical behavior: Infotainment system glitches, power windows acting erratically, or other electronic components behaving strangely.
• Key fob issues: Reduced range or intermittent functionality of the key fob, indicating low system voltage.
• Clicking sound from starter: A rapid clicking noise when attempting to start, indicating insufficient power to engage the starter motor.

At a glance: difficulty, repair cost, and diagnostic workflow

• Difficulty Rating: 6/10 — Easy to moderate
• Common Symptoms: The battery light on the dashboard illuminates, even if the battery is relatively new.; Your vehicle's remote start or keyless entry system becomes unreliable.; Aftermarket accessories (dash cams, stereo systems, etc.) appear to be drawing power even when the car is off.; The vehicle's clock or radio presets are consistently reset after sitting for a period.
• Estimated Repair Cost: $80–$900 (parts + typical shop labor)
• OEM Tooling Required: Standard OBD-II scanner and hand tools

Diagnostic workflow:

1. Confirm the symptom on your 2020 Subaru FORESTER.
2. Scan for stored or pending codes with an OBD-II tool.
3. Inspect the most common causes in this guide (visual checks first).
4. Run verification tests before replacing parts.
5. Repair, clear codes, and verify on a test drive.

Browse the model repair hub and make hub for related guides.

Symptoms and warning signs

Beyond the obvious dead battery, pay attention to these specific signs that your 2020 Subaru Forester might be suffering from a parasitic draw:

• The battery light on the dashboard illuminates, even if the battery is relatively new.
• Your vehicle's remote start or keyless entry system becomes unreliable.
• Aftermarket accessories (dash cams, stereo systems, etc.) appear to be drawing power even when the car is off.
• The vehicle's clock or radio presets are consistently reset after sitting for a period.
• A faint clicking or buzzing sound from the fuse box or under the dash after the car is off and locked.
• A noticeable drain on the battery after parking the car for only a few hours, especially in moderate temperatures where cold isn't a factor.

How to verify and confirm the issue

Confirming a parasitic draw on your 2020 Subaru Forester involves more than just checking the battery's charge. You'll need to measure the actual current draw when the vehicle is supposed to be "asleep."

1. Battery Health Check: First, ensure your battery itself isn't the problem. Charge the battery fully and then have it load-tested at an auto parts store or with a dedicated battery tester. A failing battery can mimic a parasitic draw.
2. Alternator Check: A faulty alternator might not be charging the battery properly while driving. Test the charging system voltage with the engine running; it should be between 13.5V and 14.5V.
3. Parasitic Draw Test (Multimeter Method):
   • Ensure your Forester has been off for at least 30 minutes to allow all modules to "sleep."
   • Disconnect the negative battery terminal.
   • Set your multimeter to measure Amps (A) and connect it in series between the negative battery post and the disconnected negative battery cable. The red lead goes to the cable, the black lead to the battery post.
   • Note the initial reading. It might be high at first (up to several amps) as modules wake up, but it should drop significantly after 10-20 minutes. A healthy parasitic draw for most modern vehicles is typically under 50 milliamps (0.05A). If it remains consistently above this, you have a draw.
4. Visual Inspection: Check for any lights accidentally left on (glove box, trunk, vanity mirrors), or any aftermarket accessories that are hardwired and not turning off.
5. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any stored codes. While not directly indicating a parasitic draw, codes related to specific modules (e.g., infotainment, body control module, door modules) can point to a component that might be staying awake and drawing power. For a comprehensive overview of diagnostic tools, you can visit our all repair guides section.

Common causes (most likely first)

Pinpointing the exact cause of a parasitic draw on a 2020 Subaru Forester can be challenging, but some issues are more common than others:

• Aftermarket Accessories: Non-factory installed items like dash cams, alarm systems, remote starters, or upgraded audio equipment are frequent culprits if not wired correctly or if they malfunction.
• Faulty Body Control Module (BCM) or Infotainment System: These complex electronic modules manage many vehicle functions. If they fail to enter "sleep mode" or develop an internal fault, they can continuously draw power. Subaru's Starlink system has been known to cause issues in some models.
• Stuck Relays: A relay that is stuck in the "on" position can keep a circuit energized even when the vehicle is off. Common culprits include fuel pump relays, cooling fan relays, or accessory relays.
• Dome Light/Trunk Light Switches: A faulty switch or latch mechanism can prevent these lights from turning off, leading to a slow but steady drain.
• Faulty Alternator Diode: While rare, a failing diode in the alternator can allow current to flow from the battery to the alternator even when the engine is off.
• Glove Compartment or Vanity Mirror Lights: These small lights are often overlooked but can cause a drain if their switches fail.
• Short Circuits: A damaged wire or component causing a short to ground can create an unintended path for current flow.

Related guides on this vehicle

• 2019 Subaru Outback Battery Keeps Dying: Causes & Fixes
• 2017 Impreza Battery Keeps Dying: Diagnose & Fix Drain
• 2018 Subaru Outback Battery Keeps Dying Overnight

Step-by-step diagnosis and fixes

Once you've confirmed a parasitic draw, the next step is to isolate the circuit responsible. This process typically involves systematically eliminating possibilities.

1. Prepare the Vehicle: Close all doors, trunk, and hood latches (you may need to manually depress the latch to simulate closure). Remove the key from the ignition. Wait 15-30 minutes for all modules to power down.
2. Connect Multimeter: As described above, connect your multimeter in series between the negative battery post and the negative battery cable. Ensure it's set to measure Amps (start with a higher range like 10A, then switch to mA once the draw stabilizes).
3. Record Baseline Draw: After the vehicle has "slept," note the stable current draw. Anything above 50mA (0.05A) indicates a parasitic draw.
4. Pull Fuses One-by-One: Starting with the fuse box under the hood, carefully pull one fuse at a time. After pulling each fuse, wait a few seconds and observe the multimeter reading. If the draw significantly drops when a specific fuse is removed, you've found the problematic circuit.
   • Important: Remember to reinstall each fuse before pulling the next one, unless you've identified the faulty circuit.
   • If the draw is still present after checking all under-hood fuses, move to the interior fuse box (usually under the dash on the driver's side).
5. Identify the Component: Once you've identified the circuit, consult your 2020 Subaru Forester's owner's manual or a wiring diagram to see what components are on that circuit. This will narrow down your search considerably.
6. Inspect the Component/Wiring: Visually inspect the identified components and their wiring for signs of damage, corrosion, or aftermarket modifications. Check for lights that might be staying on (e.g., glove box, trunk).
7. Test Relays: If the circuit points to a relay, you can swap it with a known good, identical relay from a non-critical circuit (e.g., horn relay) to see if the draw disappears.
8. Professional Help: If you cannot isolate the draw, or if it points to a complex module like the BCM or infotainment system, it's best to consult a professional technician who has specialized diagnostic tools and expertise with Subaru vehicles.

Repair options and cost factors

The cost to resolve a 2020 Subaru Forester battery drain problem can vary widely based on the cause:

• DIY Fixes (Low Cost): If the issue is a simple oversight like a light left on, a loose connection, or a faulty aftermarket accessory that can be disconnected, the cost is minimal (potentially just your time and a multimeter, around $20-$50).
• Component Replacement (Moderate Cost):
  • Battery: If the battery was damaged by repeated draining, a new one costs $150-$250.
  • Relay: A new relay is typically $15-$50.
  • Switch: A new door jamb, trunk, or glove box light switch might be $20-$70.
  • Alternator (if faulty diode): A new or remanufactured alternator can range from $200-$500 for the part alone.
• Module Replacement (High Cost): If a sophisticated module like the Body Control Module (BCM) or an infotainment unit is faulty, parts can be $300-$800+, plus significant labor for diagnosis, replacement, and programming.
• Professional Diagnosis: If you take your Forester to a shop, expect to pay for diagnostic time (1-3 hours at $100-$150/hour) to pinpoint the draw, in addition to the cost of parts and labor for the repair. For more model-specific information, check our Forester model hub.

When to see a professional

While many DIY enthusiasts can tackle basic parasitic draws, there are clear instances when professional help is advisable:

• Inability to Isolate: If you've followed the diagnostic steps and cannot pinpoint the source of the draw.
• Complex Module Issues: When the draw points to a critical electronic control module (e.g., BCM, infotainment system), which often requires specialized diagnostic tools and programming after replacement.
• Intermittent Problems: If the drain is inconsistent, making it difficult to replicate and diagnose.
• Safety Concerns: Any electrical work carries risks. If you are uncomfortable working with vehicle electrical systems, or if the issue involves high-current circuits, it's safer to defer to a qualified technician.

Frequently asked questions

Why does my 2020 Subaru Forester battery keep dying?

Your 2020 Subaru Forester's battery might be repeatedly dying due to a "parasitic draw," meaning an electrical component is continuously consuming power even when the vehicle is turned off. Common culprits include faulty aftermarket accessories, a module that isn't entering sleep mode, or a light that remains on unnoticed.

Can a bad alternator cause a parasitic draw on a 2020 Subaru Forester?

Yes, a bad alternator can indirectly contribute to a battery drain. Specifically, a failing rectifier diode within the alternator can allow current to flow from the battery back into the alternator when the engine is off, effectively creating a parasitic draw. This is less common than other causes but is a possibility to consider during diagnosis.

How long should a 2020 Subaru Forester battery last?

Under normal conditions, a typical car battery in a 2020 Subaru Forester should last between 3 to 5 years. Factors like extreme temperatures, frequent short trips, and consistent deep discharges (due to parasitic draws) can significantly shorten its lifespan. Regular battery health checks can help extend its life.

Sources and further reading

For additional diagnostic information, consult your 2020 Subaru Forester's owner's manual or a reputable automotive repair database.

Disclaimer: This article provides general information and is not a substitute for OEM service procedures or the advice of a qualified technician. Always use a qualified technician for safety-critical work.