Subaru Battery Drain Parasitic Draw Test

By the Radman Auto Repair team, independent auto repair in Etobicoke since 1999 · Updated November 2026

Many 2015–2020 Subaru Outback, Legacy, Forester, WRX and Ascent owners have had batteries go flat after the car sits a day or two. A module that stays awake, a small original battery, or short trips that never fully charge it can all cause it. A parasitic draw test finds out which.

Symptoms

What Causes It

Before You Start

• Park on level ground, set the parking brake and chock the wheels. Never work under a car held up only by a jack: use rated jack stands.
• Let the engine and exhaust cool before you touch them; coolant systems are under pressure when hot.
• Wear safety glasses and gloves, and disconnect the 12V battery before unplugging electrical parts or working near airbags.
• Check for open recalls on your VIN (Transport Canada or the manufacturer’s site) before you buy parts: a recall repair is free at the dealer.
• Set the meter to the 10A range first and don’t crank the engine with the meter in series; you’ll blow the meter fuse.
• Keep the doors “closed” (latch the latches with a screwdriver) so the car can sleep during the test.

Step-by-Step: Subaru Battery Drain

1. Charge and test the battery. Fully charge the battery and test it. Replace it if it fails.
2. Remove accessories. Unplug dash cams and chargers from the power outlets.
3. Prepare the car. Open the hood, latch the door latches so the car thinks they are closed, lock it, and remove the key from range.
4. Connect the meter. Disconnect the negative battery cable and connect the multimeter in series between the cable and the battery post.
5. Let it sleep. Wait 30–60 minutes for the modules to go to sleep, then read the current.
6. Compare to normal. A healthy car usually draws well under 50 milliamps when asleep; much more points to a draw.
7. Pull fuses. Pull fuses one at a time and watch the meter. When the current drops, you’ve found the circuit.
8. Fix and recheck. Repair the fault on that circuit, then ask a Subaru dealer about software updates for your VIN.

When to Stop and Bring It In

• The draw is on a circuit you can’t trace, such as a module.
• The battery keeps dying with a normal draw: the charging system may be weak.
• You think your car may be covered: ask a Subaru dealer.
• You need a module or software update: see battery drain diagnosis.

Not sure, or out of time? Radman Auto Repair in Etobicoke does this repair every week. Book online or call (416) 742-4521.

Also Known As

Owners search for “Subaru battery keeps dying”, “Outback dead battery”, “Forester battery drain”, “Ascent battery dying”, “Subaru parasitic drain” or “Subaru battery class action”. The test is a parasitic draw (key-off current) test.

Frequently Asked Questions

See also Battery Drain Diagnosis, Battery Test & Replacement, Electrical Diagnostics, DIY Repair Guides by Manufacturer.

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