How to Test a Car Battery With a Multimeter
3 lessons in this series, 6 min in total
- Signs Your Car Battery Is Dying 2 min read
- How to Test a Car Battery With a Multimeter 2 min read
- Should You Charge or Replace a Weak Car Battery? 2 min read
Steps come from Interstate Batteries’ how-to and FAQ, and the chart from Battery University’s BU-903 page, plus AAA’s replacement point and Optima’s REDTOP figure. More on how we research.
How to take an accurate reading
Resting voltage is the battery’s voltage after it has sat with nothing charging or drawing from it. Before you measure, make sure the cables are tight and the terminals clean (see the clicking and warning-light signs).
- Let the battery rest. Battery University (BU) says at least four hours with nothing charging it; battery makers recommend 24 hours for lead acid.
- Remove surface charge if needed. Surface charge is a temporary boost from a recent drive or charge that makes the reading look high. Interstate says to run the headlights for about two minutes, then switch them off.
- Set the meter to DC volts, on the 0-20 V range.
- Touch red to positive (+) and black to negative (-).
- Read the voltage and compare it with the chart below.
- Start the engine and read again. Interstate’s how-to wants more than 13 V, and its FAQ gives 13.7-14.7 V. Lower could mean a bad alternator or a bad battery.
Car battery voltage chart
State of charge is how full the battery is, as a percentage. BU’s chart, based on the Battery Council International standard, is for a 12 V flooded starter battery read at about 78°F (26°C) after a 24-hour rest.
| State of charge | Resting voltage | What it means |
|---|---|---|
| 100% | 12.65 V | Fully charged |
| 75% | 12.45 V | Partly drained |
| 50% | 12.24 V | Half drained |
| 25% | 12.06 V | AAA: replacement typical below 25% |
| 0% | 11.89 V | Empty (dead) |
| Engine running | 13.7-14.7 V | Normal range in Interstate’s FAQ |
Figures differ by source: AAA puts 25% around 11.8 V at 80°F (27°C), not BU’s 12.06 V, and Interstate calls 11.9 V or below dead. BU says heat raises the reading and cold lowers it, and AGM batteries read slightly higher, per BU. Optima, which makes AGM batteries, puts a fully charged REDTOP at about 12.6-12.8 V.
To see where a dash cam’s low-voltage cutoff falls on this chart, read does dash cam parking mode drain your battery.
What the reading can’t tell you
Interstate says a good resting reading doesn’t mean you have a good battery. AAA adds that a battery can show a full charge and still have internal damage.
A low reading after a proper rest says the battery needs a charge, whatever its condition. A full reading on a battery that still cranks slowly or needs jumps doesn’t clear it: voltage alone can’t prove a battery healthy.
A low engine-running reading could mean a bad alternator or a bad battery, per Interstate. A conductance or load test at a shop gives the clearer answer.
If your reading is low, decide whether to charge or replace a weak battery.
