2017 Subaru Forester Battery Dying Fast: Fix Excessive Drain

What drivers notice on this 2017 Subaru Forester

Many 2017 Subaru Forester owners experience the frustrating problem of their battery dying fast, often after the vehicle has been parked for just a day or two. This isn't just an inconvenience; it can leave you stranded, requiring a jump start or even a new battery sooner than expected. The issue typically manifests as a slow crank, dim lights, or a completely dead battery when you try to start the car, indicating an excessive battery drain or "parasitic draw" even when the vehicle is turned off.

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

• Difficulty Rating: 6/10 — Easy to moderate
• Common Symptoms: Slow or sluggish engine cranking: The engine struggles to turn over when you try to start it.; Completely dead battery: The car won't start at all, and there's no power to accessories.; Needing frequent jump starts: You find yourself needing to jump-start your Forester regularly.; Dim interior or exterior lights: Headlights, dash lights, or dome lights appear unusually dim.
• 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 2017 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

If your 2017 Subaru Forester battery is dying fast, you'll likely notice one or more of these symptoms:

• Slow or sluggish engine cranking: The engine struggles to turn over when you try to start it.
• Completely dead battery: The car won't start at all, and there's no power to accessories.
• Needing frequent jump starts: You find yourself needing to jump-start your Forester regularly.
• Dim interior or exterior lights: Headlights, dash lights, or dome lights appear unusually dim.
• Battery warning light: The battery light on your dashboard might illuminate, though this usually indicates a charging system issue rather than a parasitic draw.
• Unusual electrical behavior: Features like the infotainment system or power windows might act erratically before the battery completely drains.

How to verify and confirm the issue

Confirming that your 2017 Subaru Forester battery is dying fast due to an excessive draw requires systematic checks:

• Battery Voltage Test: With the engine off, a fully charged 12V battery should read 12.6-12.8V. Consistently below 12.4V after charging suggests a weak battery or a draw.
• Charging System Test: Engine running, voltage across terminals should be 13.5V to 14.5V. Outside this range indicates an alternator issue.
• Parasitic Draw Test:
  1. Ensure all doors are closed, lights are off, and the key is out of the ignition. Allow the vehicle to "go to sleep" (this can take 15-30 minutes on modern Subarus).
  2. Disconnect the negative battery terminal.
  3. Connect a multimeter in series between the negative battery post and the disconnected negative battery cable, set to measure amperage (amps).
  4. A normal parasitic draw for a 2017 Subaru Forester should be less than 50 milliamps (0.05 amps). If your reading is significantly higher (e.g., 0.2 amps or more), you have an excessive draw.
• Visual Inspection: Check for corroded battery terminals, loose connections, or improperly wired aftermarket accessories.
• OBD-II Scan: While not directly indicating a parasitic draw, an OBD-II scanner can reveal diagnostic trouble codes (DTCs) related to power management or specific modules that might not be shutting down correctly. For example, codes related to the body control module (BCM) or infotainment system could point to a culprit.

Common causes (most likely first)

Several factors can cause your 2017 Subaru Forester battery to die fast:

• Aging or Weak Battery: The most common culprit. Even without a parasitic draw, an older battery simply loses its ability to hold a charge effectively, especially in extreme temperatures. Subaru factory batteries sometimes have a shorter lifespan than expected.
• Parasitic Draw from Electrical Components:
  • Infotainment System (Starlink): The Starlink system in 2017 Subarus can sometimes fail to fully power down, leading to a constant draw. This is a known issue for some owners.
  • Aftermarket Accessories: Improperly installed dash cams, alarms, remote starters, or audio systems can draw power even when the car is off.
  • Interior Lights/Trunk Light: A dome light left on, or a trunk light switch that's stuck or faulty, keeping the light on.
  • Glove Box Light: Similar to the trunk light, a faulty switch can keep it illuminated.
  • Relays Stuck Open: A relay that's stuck in the "on" position can continuously power a circuit.
  • Body Control Module (BCM): A malfunctioning BCM can fail to send proper shutdown signals to various systems.
• Faulty Alternator: While usually causing charging issues while driving, a diode failure in the alternator can sometimes allow current to drain back through it when the engine is off.
• Corroded or Loose Battery Terminals: These can prevent the battery from fully charging or delivering consistent power.
• Key Fob Left in Range: Some keyless entry systems can keep certain modules awake if the key fob is left too close to the vehicle for extended periods.

Related guides on this vehicle

• 2021 Subaru Outback Battery Keeps Dying: Diagnosis & Fixes
• 2020 Subaru Forester Battery Drain Problem Diagnosis
• 2019 Subaru Outback Battery Keeps Dying: Causes & Fixes

Step-by-step diagnosis and fixes

Once an excessive draw is confirmed, here's how to pinpoint the source:

1. Charge and Test Battery: Fully charge your battery and have it load tested at an auto parts store. If it fails, replace it. Even a new battery can quickly die if there's an underlying draw.
2. Perform Parasitic Draw Test: Use a multimeter as described in the verification section above.
3. Isolate Circuits (Fuse Pull Method):
   • With the multimeter still connected and showing an excessive draw, begin pulling fuses one by one from the fuse box (under the hood and inside the cabin).
   • Watch the multimeter reading. When the amperage drops significantly after pulling a specific fuse, you've identified the circuit causing the draw.
   • Important: After pulling each fuse, wait a few seconds for the system to react. Reinsert the fuse before pulling the next one unless you've found the culprit.
4. Investigate the Culprit Circuit: Once you've narrowed it down to a specific fuse, consult your 2017 Subaru Forester owner's manual or a service manual to identify which components are on that circuit. For example, if the "AUDIO" fuse reduces the draw, focus on the infotainment system, amplifier, or related wiring.
5. Check Alternator Diodes: If the draw doesn't drop significantly with any fuse, disconnect the main power wire from the alternator. If the draw disappears, your alternator likely has a faulty diode.
6. Inspect Wiring and Connections: Look for frayed wires, exposed insulation, or corroded connectors, especially around aftermarket installations.
7. Test Relays: If a circuit is drawing power, try swapping relays with known good ones from a non-critical circuit to see if the draw stops.

For more general repair guidance, you can explore our All repair guides.

Repair options and cost factors

The cost to fix a 2017 Subaru Forester battery dying fast varies widely depending on the root cause:

• Battery Replacement: $100–$250. This is often the first step, especially if your battery is old or weak.
• Alternator Replacement: $300–$700 for parts and labor.
• Diagnosing Parasitic Draw: If you take it to a shop, diagnosis alone can be $100–$200, as it's time-consuming.
• Replacing Faulty Component (e.g., infotainment unit, BCM, relay): This can range from $50 for a simple relay to $500+ for a complex module like the BCM or infotainment system, plus labor.
• Wiring Repair: $50–$300 depending on complexity.

Performing the diagnostic steps yourself can save significant labor costs. Remember to check out our Subaru vehicle hub for more specific information related to your make.

When to see a professional

While many diagnostic steps for a parasitic draw can be performed by a DIY owner, there are times when professional help is essential:

• Persistent, Undiagnosed Draw: If you've followed the steps and can't pinpoint the source of the draw.
• Complex Electrical Issues: If the issue seems to stem from a major module (BCM, infotainment) or involves intricate wiring.
• Specialized Tools Required: Some advanced diagnostics might require specific OEM scan tools beyond a standard OBD-II scanner or advanced electrical testing equipment.
• Safety Concerns: If you're uncomfortable working with vehicle electrical systems, especially around high current.
• Warranty: If your 2017 Subaru Forester is still under warranty, a dealership visit is often the best course of action.

Frequently asked questions

Why does my 2017 Subaru Forester battery keep dying even after replacement?

If your 2017 Subaru Forester battery keeps dying even after being replaced, it almost certainly indicates an underlying issue like a parasitic draw or a faulty charging system. The new battery is simply being drained by a component that isn't shutting off, or it's not being recharged properly by the alternator. A parasitic draw test is crucial to identify the culprit.

How long should a 2017 Subaru Forester battery last?

Typically, a car battery is expected to last between 3 to 5 years. However, factors like extreme temperatures, frequent short trips, and excessive parasitic draws can significantly shorten its lifespan. If your 2017 Forester battery is failing prematurely, it's a strong sign of an underlying electrical problem.

Can a faulty infotainment system cause battery drain in a 2017 Subaru Forester?

Yes, a faulty infotainment system, particularly the Starlink unit in some 2017 Subaru Foresters, is a known potential cause of excessive battery drain. If the unit doesn't fully power down or gets stuck in a boot loop, it can continuously draw power, leading to a dead battery. This can often be identified during a parasitic draw test when pulling the associated fuse.

Sources and further reading

• Browse vehicles
• Forester model hub

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