Voltage of a fully charged 12V battery
The short answer
A conventional 12-volt lead-acid car battery that is fully charged and has rested with no load or charger connected typically measures about 12.6 to 12.7 volts. The "12V" label is a nominal rating. A healthy, fully charged battery sits slightly above 12 volts, and a reading of exactly 12.0 volts usually means the battery is substantially discharged.
That figure has three important qualifications. It applies to resting voltage, not voltage while charging. It depends on battery chemistry. It is commonly quoted for a battery at around room temperature, about 25°C (77°F).
How battery chemistry changes the number
Most vehicles use one of several battery types, and each reaches a slightly different resting voltage when full. The ranges below are general industry figures. Exact values vary by manufacturer, so the battery label or the maker's datasheet takes precedence.
Battery type | Typical resting voltage when fully charged; Flooded (standard wet-cell) lead-acid | About 12.6 to 12.7 V; EFB (enhanced flooded battery, common in start-stop vehicles) | About 12.6 to 12.7 V; AGM (absorbent glass mat) lead-acid | About 12.8 to 12.9 V; Gel lead-acid | About 12.8 V; Lithium iron phosphate (LiFePO4) 12V | About 13.3 to 13.4 V
Lithium 12V batteries behave differently from lead-acid. Their voltage stays nearly flat across much of the discharge range, so a resting reading is a less precise guide to their state of charge than it is for lead-acid batteries.
Resting voltage versus charging voltage
With the engine running, a meter across the battery terminals shows the charging system's output, not the battery's own resting state. That output is typically around 13.7 to 14.7 volts, depending on the vehicle and its charging strategy. Some modern vehicles with smart alternators intentionally vary this voltage. A reading in that range while driving is normal and does not mean the battery holds that voltage on its own.
Right after driving or charging, a lead-acid battery also carries a temporary surface charge. This makes it read higher than its true resting value. For an accurate reading, let the battery sit for several hours with no load or charger connected. A common alternative is to switch on the headlights for about a minute, turn them off, and then measure.
Reading lower values on a lead-acid battery
For a standard flooded battery at rest, commonly cited approximate state-of-charge points are as follows. AGM batteries run slightly higher at each level.
About 12.6 to 12.7 V: fully charged; About 12.4 V: roughly 75 percent charged; About 12.2 V: roughly 50 percent charged; About 12.0 V: roughly 25 percent charged; Below about 11.9 V: essentially discharged
Cold temperatures lower the reading slightly, so a battery measured on a freezing morning may show a little less than the same battery in mild weather.
What resting voltage does not tell you
Resting voltage shows state of charge, not overall battery health. An aging battery can show 12.6 volts and still fail under the heavy current draw of starting an engine. Judging whether a battery can still deliver its rated cranking performance requires a load test or a conductance tester, which many parts retailers and workshops offer.
Gaps and how to fill them
No manufacturer-specific specifications or test data were provided for this guide, so the figures above are general ranges rather than values for any particular battery, vehicle, model year or market. For a specific battery, the most reliable sources are the voltage and charging information on its label, its datasheet, or the vehicle owner's manual. This matters most for AGM, EFB and lithium batteries in vehicles with battery management systems.