Turn off the car and all accessories
Set the multimeter to DC volts
Connect the red probe to the battery’s positive terminal
Connect the black probe to the battery’s negative terminal
Read the voltage on the multimeter
Check for about 12.6 volts or higher for a fully charged battery
Check for about 12.4 volts for a partially charged battery
Check for about 12.2 volts or lower for a weak battery
Start the car and read the voltage again
Check for about 13.7 to 14.7 volts with the engine running
Replace the battery if the readings are consistently low or unstable