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2023 Legacy Battery Draining Overnight - Parasitic Draw?

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Ryan M. · rep 0 · May 22, 3:20 AM · 1 replies · solved · Question

Vehicle: 2023 Subaru Legacy Limited

I bought a new 2023 Subaru Legacy Limited about 8 months ago, and I've already had the battery die on me twice overnight. Both times, I had to get a jump start. There's nothing obvious left on, like interior lights or the radio. I don't have any aftermarket accessories installed, just the factory setup.

It's incredibly frustrating to wake up to a dead car, especially with a relatively new vehicle. Could this be a faulty battery, or is there something else draining power? I'm worried about getting stranded. What's the best way to figure out what's going on here?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:20 AM

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ClearTheCode admin answer:

Experiencing a dead battery twice in a new 2023 Subaru Legacy is definitely not normal and points to either a faulty battery or a parasitic draw. Given the vehicle's age, a parasitic draw is a strong suspect, but the battery itself should also be thoroughly tested.

  1. Battery Health Test: The first step is to have the battery tested. Even new batteries can sometimes be defective. A professional battery test will check its cold cranking amps (CCA) and overall health. If the battery is weak, it may not hold a charge adequately.
  2. Parasitic Draw Test: If the battery tests good, a parasitic draw test needs to be performed. This involves connecting an ammeter in series with the battery's negative terminal and measuring the current draw when the car is fully off and all systems are asleep. A healthy draw is typically under 50 milliamps (0.05 amps). If it's higher, individual fuses can be pulled to isolate the circuit causing the draw.
  3. Check for Software Glitches: Modern vehicles have many modules that stay active after shutdown. Sometimes, a software glitch in a module (e.g., infotainment, telematics, keyless entry) prevents it from entering 'sleep' mode, leading to a continuous draw.

Common Causes:

  • Faulty Battery: A new battery can still have an internal defect that prevents it from holding a charge.
  • Stuck Relay: A relay that fails to open can keep a circuit powered, even when the car is off.
  • Faulty Module: A control module (e.g., infotainment, telematics unit, body control module) that doesn't properly shut down can continuously draw power.
  • Alternator Issues: While less likely for an overnight drain, a failing alternator might not be fully charging the battery during operation, leading to a gradual discharge.

When to See a Shop:

  • You should take your 2023 Legacy to a Subaru dealership immediately. Since the car is new, it's under warranty, and they are best equipped to diagnose and repair this issue. They have specialized tools to perform accurate parasitic draw tests and can check for any relevant TSBs or software updates related to battery drain. Documenting the incidents is important for warranty claims. Driving with a repeatedly drained battery can also shorten its lifespan and potentially damage other electrical components.
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