Turn off the engine and all accessories
Set a multimeter to DC volts
Place the red probe on the positive battery terminal
Place the black probe on the negative battery terminal
Read the voltage
Check for about 12.6 volts on a fully charged battery
Check for about 12.4 volts on a partially charged battery
Check for 12.2 volts or less on a weak battery
Have someone start the car while watching the meter
Check that cranking voltage does not drop below about 9.6 volts
Start the engine and measure charging voltage
Check for about 13.7 to 14.7 volts with the engine running
Inspect the battery case and terminals for corrosion, leaks, or damage
Use a battery load tester if available
Compare the load test result to the battery’s rated specifications
Replace the battery if it fails the voltage or load test