How Many Volts Should a Car Battery Have? (In Different Situations), by More Automotive on YouTube. 10 min 56 s.
- Video length
- 10 min 56 s
- Time to do it
- 20 minutes
- Difficulty
- Easy
- Steps
- 9
What you need
Steps
Park on a level surface, turn the engine off and switch off all lights and accessories. Let the battery rest for a few hours, or overnight, before you test it.
Set your digital multimeter to DC volts. Pick the 20V range on a manual meter, or leave it on auto, then touch the probes together to confirm it reads zero.
Connect the red probe to the positive terminal and the black probe to the negative terminal. Press each probe gently so it bites through any dirt or corrosion.
Read the resting voltage. A fully charged battery shows 12.6 to 12.7 volts. About 12.4 volts is roughly 75 percent charged, 12.2 volts about half, and 12.0 volts about a quarter.
Ask a helper to crank the engine while you watch the meter. A normal start pulls the reading down to about 10 to 11 volts, then it climbs back up.
Start the engine and read the voltage at the battery again. A conventional charging system should show around 13.5 to 14.7 volts at idle.
Switch on the headlights, blower fan and rear defroster, then rev the engine gently. The reading should stay above about 13 volts. A big drop points to a weak alternator.
If the battery reads 12.6 volts but the car still struggles to start, have it load tested. A load test and a cold cranking amp (CCA) check show its true condition.
Charge a low battery with a smart charger rated for your battery size, then retest it. Never charge a frozen battery or one with a cracked case.
Tips and common mistakes
Probe the battery posts themselves, not the clamp bolts, so a poor connection does not hide the real reading.
Cold weather lowers voltage, so a reading taken in freezing conditions can look worse than the battery really is.
Many modern cars use smart charging, so the voltage may swing between about 12 and 15 volts, which can be normal.
Keep the cranking test short, around 10 to 15 seconds, and let the starter cool between attempts.
Questions
What should a healthy 12V car battery read?
About 12.6 to 12.7 volts at rest with the engine off. With the engine running it should sit around 13.5 to 14.7 volts on a conventional charging system.
Why does my battery show 12.6 volts but the car will not start?
The voltage can look fine while the battery has lost its ability to deliver current. A load test or CCA check will show whether it needs replacing.
What voltage means the alternator is failing?
Below about 13 volts with the engine running and accessories on is a warning sign. Above roughly 15 volts can mean overcharging, which also needs checking.
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.
