How to Test a Car Battery With a Multimeter
Reviewed by GarageDex editorial
GarageDex's guide to testing a battery with a basic multimeter in three readings: at rest, while cranking, and with the engine running. A resting voltage alone is not a verdict, because a battery can read 12.6 volts and still collapse under the load of a starter. The cranking reading is the one that catches a battery on its way out.
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- Set the multimeter to DC volts (V with a straight line), 20 V range if it is not auto-ranging.
- Remove surface charge: if the car ran in the last few hours, turn the headlights on for one minute, then off, and wait a minute.
- Resting test: engine off, red probe on the positive (+) post, black on the negative (-). 12.6 V or higher is fully charged; 12.4 V is about 75 percent; 12.2 V about 50 percent; 12.0 V about 25 percent; below 11.9 V is discharged.
- Cranking test: have someone start the engine while you watch the meter. The voltage will dip; if it drops below about 9.6 V at normal temperature, the battery is weak under load even if it read fine at rest.
- Charging test: with the engine running and accessories off, read the battery again. 13.7 to 14.7 V means the alternator is charging. Under 13.2 V or over 15 V points to the charging system, not the battery.
Reading the numbers
| Resting voltage (engine off) | State of charge |
|---|---|
| 12.6 V or higher | 100 percent |
| 12.4 V | About 75 percent |
| 12.2 V | About 50 percent |
| 12.0 V | About 25 percent |
| Below 11.9 V | Discharged; charge it before judging it |
Cranking: stays above about 9.6 V at room temperature on a healthy battery. Charging: 13.7 to 14.7 V with the engine running. AGM batteries rest slightly higher than flooded ones (a full AGM is often 12.8 to 12.9 V), so use the same thresholds but expect the top end.
What you need
Any digital multimeter that reads DC volts. A dedicated battery tester gives a cold-cranking-amp result instead of a voltage guess and is worth it if you look after several vehicles.
Tools used in this guide
- Digital multimeterAuto-ranging DC volts is all this test needsView on Amazon
- Car battery load testerReads cold cranking amps and charging-system health in one testView on Amazon
These tools fit any vehicle. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.
A discharged battery is not a bad battery yet
If it reads under 12.2 V, charge it fully first and let it rest a few hours, then re-test. A battery that comes back to 12.6 V and holds it overnight was just flat. One that drops back to 12.2 V or lower by morning, with nothing connected, has a dead cell or heavy sulfation and is done. See cold cranking amps explained for what the rating on the label means.
When it is time to replace it
Look up the group size, CCA and type (AGM or flooded) for your year, make and model. Fitting an AGM where the car specifies one matters on cars with start-stop, and some cars need the new battery registered to the charging system.
Frequently asked
What voltage should a car battery be?
About 12.6 volts or a little more at rest, fully charged and after the surface charge is gone. 12.4 V is roughly three-quarters charged, 12.2 V half, 12.0 V a quarter, and under 11.9 V is discharged. With the engine running you should see 13.7 to 14.7 V from the alternator.
Can a battery read 12.6 volts and still be bad?
Yes. Resting voltage measures state of charge, not the battery's ability to deliver current. A battery with a worn or sulfated plate can hold voltage with nothing connected and then fall below 9.6 V the moment the starter loads it. That is why the cranking test matters.
How do I know if it is the battery or the alternator?
Engine running: 13.7 to 14.7 V at the battery means the alternator is doing its job, so a battery that keeps going flat is the problem. Under about 13.2 V running, or a reading that does not rise above the resting voltage, means the alternator is not charging and a new battery will go flat too.
Is a multimeter test as good as a load test at the parts store?
The cranking reading is a rough load test. A parts-store tester applies a controlled load or measures conductance and compares it to the battery's rated cold cranking amps, which is more precise, and it is usually free. Use the multimeter to decide whether the trip is worth it.
Need your car's exact spec?
Find the replacement battery size for your car