How to Check Your Car Battery, by Alex Morales on YouTube. 1 min 21 s.
- Video length
- 1 min 21 s
- Time to do it
- 10 minutes
- Difficulty
- Easy
- Steps
- 8
What you need
Steps
Park on level ground and switch the engine off. Take the keys out, then put on safety glasses and gloves before you open the hood.
Find the battery using your owner's manual. Some cars put it in the trunk or under a seat. Note which post is positive (+) and which is negative (-).
Look over the case for white or blue-green crust, cracks, swelling or wet spots. If the battery is cracked, leaking or swollen, do not touch it and have a mechanic check it.
Wiggle each cable clamp by hand. A clamp that moves needs tightening with a wrench, and heavy corrosion should be scrubbed off with a wire brush and a baking soda and water paste.
Set the multimeter to DC volts, 20V range or auto. Switch on the headlights for about 30 seconds, then turn them off to clear the surface charge.
Touch the red probe to the positive post and the black probe to the negative post. Hold both steady and read the number on the screen.
Read the result. About 12.6V means a full charge, 12.4V is roughly 75 percent, 12.2V is about half, and below 12.0V means the battery is discharged.
Charge a low battery with a smart charger and retest it after it rests. If it drops again or will not hold a charge, have it load tested at an auto parts store.
Tips and common mistakes
Never let a wrench or probe touch both posts at once, since that creates sparks near flammable battery gas.
Check the battery before winter and before a long trip, not only when the car cranks slowly.
A battery that reads fine but still cranks slowly may have a charging problem, so have the alternator tested too.
Let the battery sit for an hour after charging before you trust the voltage reading.
Questions
What voltage means a car battery is bad?
A resting reading below 12.0V means it is discharged, and below about 12.2V it is only half charged. If it will not hold above 12.4V after a full charge, it is likely failing.
Can I check the battery with the engine running?
You can, but that reading shows the alternator output, usually 13.5V to 14.5V. Test with the engine off first to see the battery's own charge.
Do I need to disconnect the battery to test it?
No. Leave the cables connected and touch the probes to the posts. Check your owner's manual first if your car has special shutdown steps.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
