Quick answer
With the engine off and the battery rested, a healthy, fully charged 12V car battery typically reads about 12.6 to 12.8 volts. With the engine running, the charging system usually brings the reading up to roughly 13.7 to 14.7 volts. Exact figures vary a little by battery type, temperature and manufacturer, so treat these as general guidance.
Car battery voltage chart
These are approximate resting readings (engine off, no loads, after the car has sat for a while):
| Resting voltage | Approximate state of charge | What it suggests |
|---|---|---|
| 12.6 to 12.8 V | About 100% | Fully charged |
| About 12.4 V | About 75% | Acceptable, may benefit from charging |
| About 12.2 V | About 50% | Needs recharging |
| About 12.0 V or lower | 25% or less | Discharged; may struggle to start the car |
| Around 10.5 V or lower | Deeply discharged | Possibly damaged or failed cells |
AGM and other types can read slightly differently, so check the battery maker’s information if you need precision. For the differences between constructions, see car battery types compared.
Voltage while the engine is running
When the alternator is working, the reading at the battery is commonly in the range of about 13.7 to 14.7 volts. Interpreting results:
- Under about 13 volts while running: The charging system may be undercharging.
- Above about 15 volts: The voltage regulator may be overcharging, which can shorten battery life.
Some modern cars vary charging voltage on purpose to save fuel, so a reading outside the range is a prompt to investigate, not proof of a fault.
Voltage while cranking
Voltage drops while the starter is turning. A figure of about 9.6 volts is commonly cited as the floor during cranking for a healthy, well-charged battery at normal temperatures (it can dip lower in the cold); a much lower dip suggests a weak battery or poor connections. This is easiest to check with a helper turning the key while you watch the meter, or at a shop with a load tester.
How to check battery voltage
- Turn the engine and all accessories off. For the most accurate resting reading, let the car sit for several hours, because a recent drive or charge can give a falsely high “surface charge” reading.
- Set a digital multimeter to DC volts (the 20V range if it has ranges).
- Touch the red probe to the positive terminal and the black probe to the negative terminal.
- Read the display and compare it to the chart.
- For a running test, start the engine and repeat. Keep hands and loose items away from belts and fans.
Is 11.7 volts a dead battery? What about 10.5?
A resting reading of 11.7 volts means the battery is heavily discharged. It may recover with a proper charge, but if it does not hold charge afterward it may need replacing. A reading near 10.5 volts suggests a deeply discharged or possibly damaged battery, and it is normal for that battery to fail to start the car. If you see such a reading, charge it fully and then have it tested before relying on it.
Bad battery or bad alternator?
A rough guide:
- Car starts after a jump but dies soon after, or the running voltage stays low: suspect the alternator or charging circuit.
- Car runs fine when started, but will not start after sitting, and running voltage looks normal: the battery may be worn or something is draining it.
Because symptoms overlap, a shop test of both parts is the most reliable approach. The way these two parts work together is explained in what a car battery does.
Checking for a parasitic draw
A parasitic draw is current used when the car is off. Some draw is normal for memory and security systems, but a larger one can flatten a battery overnight. Testing involves measuring current in series with the battery cable using a meter and waiting for the modules to go to sleep, which can take a while. If you are not comfortable doing this safely, ask a professional.
Is a 12V car battery AC or DC?
A car battery is DC (direct current). Current flows in one direction, from the battery’s positive terminal through the circuit and back to the negative terminal. The alternator generates AC internally, but a built-in rectifier converts it to DC before it charges the battery or powers the car. If you want to run a household AC appliance from a car, you generally need a power inverter, and 12V DC items should not be connected to AC supplies.
A “12V” battery is nominal. Six cells of about 2.1 volts each give the roughly 12.6 volts seen when it is fully charged.