How many volts is a dead car battery?
A typical car battery is a 12-volt lead-acid unit. A healthy resting battery usually reads about 12.6 to 12.8 volts. When a battery is considered dead or unable to start the engine, its resting voltage commonly falls to around 12.0 volts or lower, and heavily discharged packs can sit in the 10 to 11-volt range. With the engine running, the charging system should push the voltage to roughly 13.8 to 14.4 volts.
Understanding what voltage says about a battery
Voltage readings depend on whether the engine is off or running, and whether the battery is under load. Here is a quick guide to common resting voltage ranges and what they imply about charge level:
- 12.6–12.8 V: Fully charged, healthy battery at rest
- 12.4–12.6 V: Adequately charged (roughly 75–100% state of charge)
- 12.0–12.3 V: Partially discharged (about 50–75% state of charge); may recover with a longer or higher-quality charge
- 11.8–11.9 V: Heavily discharged; starting the engine could be difficult
- 10.5–11.0 V: Critically discharged; battery is unlikely to start a car and may be damaged
- Below about 10.5 V: Very likely damaged or sulfated; replacement recommended
Reading voltage alone doesn’t tell the whole story. A battery can show a reasonable resting voltage yet fail under load, so a proper load test or a professional evaluation is often needed to confirm health.
Why readings can vary and what to check
Several factors can affect voltage readings, including temperature, how recently the battery was charged, and whether it has cooled down after use. Measure across the battery terminals with the engine off and the car rested for at least 15 minutes to get an accurate resting voltage. If the engine is running, a healthy charging system should show about 13.8–14.4 volts; lower readings can indicate a charging problem or an electrical drain.
What to do if your battery seems dead
If your car won’t start, it’s important to approach safely and systematically. The steps below help determine whether you’re dealing with a simple discharge, a failed alternator, or a more serious battery problem:
- Attempt a safe jump-start using another vehicle or a portable jump pack
- After starting, keep the engine running and drive for 20–30 minutes to help recharge, or use a compatible charger
- If the car starts only after a jump and then dies again, or the voltage remains low after charging, the battery may be bad and require replacement
- If the battery seems fine but the car won’t start, have the alternator and charging system tested by a professional
In any case, if a battery repeatedly drops below about 12V at rest or fails to hold a charge, replacement is typically the most reliable long-term solution. Ignoring a weak battery can leave you stranded.
Summary
For a standard 12-volt lead-acid car battery, healthy resting voltage sits around 12.6–12.8 V. A “dead” battery usually measures about 12.0 V or lower at rest, with heavily discharged cells potentially around 10–11 V. The engine running should show 13.8–14.4 V if the alternator is charging properly. Always confirm with a load test if you suspect a problem, and consider replacement or professional service if the battery cannot hold a charge or the alternator is faulty.
