How many volts does a Subaru need to start?
Subarus start with a 12-volt electrical system. A healthy resting battery should read about 12.6 volts, and during cranking the voltage should stay around 9–10 volts or higher. When the engine runs, the alternator typically charges the system to about 13.8–14.4 volts to keep the battery topped up.
In practical terms, this means the car’s battery and charging system must be in good condition to ensure reliable starts. Most Subaru models use a 12-volt lead-acid battery (often AGM) to supply the starter and electronics, while the high-voltage battery is used for propulsion only in hybrids and electric models. The following details explain the numbers and how they apply to starting.
Voltage basics for starting a Subaru
Before diagnosing a starting issue, here are the essential voltage benchmarks you should know.
- 12-volt system: Conventional Subaru gasoline and diesel engines rely on a 12V battery and starter motor.
- Fully charged resting voltage: A healthy off battery should read about 12.6V to 12.8V.
- Voltage during cranking: The voltage can dip while the starter draws current; a typical minimum is about 9V to 10V for reliable cranking.
- Charging voltage when running: The alternator usually maintains roughly 13.8V to 14.4V to keep the battery charged.
- Impact of temperature and age: Cold weather and aging batteries reduce available voltage and cranking power.
Conclusion: If your resting voltage is around 12.6V and it stays above about 9–10V during cranking, starting should be reliable. If it dips lower, the battery or connections may be the issue.
Practical steps to assess starting voltage
If you suspect a voltage problem is causing a start failure, use these steps to diagnose safely and effectively.
- Turn the car off and ensure all accessories are off; allow the battery to settle for a moment before measurement.
- Measure resting voltage across the battery terminals with a digital multimeter (DMM); aim for about 12.6V.
- Have someone crank the engine and watch the voltage; note how low it drops. It should not fall below roughly 9–10V.
- Inspect battery terminals for corrosion and ensure the connections are tight and clean.
- Check the alternator belt and test the charging voltage when the engine is running (13.8–14.4V is typical).
- If the battery cannot hold charge or consistently dips under load, consider a battery replacement or a professional load test.
Conclusion: Regularly checking resting and cranking voltages, along with battery condition and charging performance, helps prevent starting problems and pinpoints weak components.
Summary
In essence, a Subaru’s start hinges on a solid 12-volt system. A healthy battery should read about 12.6 volts at rest, stay above ~9–10 volts under cranking, and be supported by an alternator delivering ~13.8–14.4 volts when the engine runs. If you encounter hard starts or no starts, measure resting and cranking voltages, inspect battery terminals and condition, and verify the charging system. Regular maintenance of the battery and connections ensures dependable starts across seasons.
