How To Test Car Battery Resting Voltage (Check It Yourself In 2 Minutes), by Simple Mechanic Advice on YouTube. 2 min 39 s.
- Video length
- 2 min 39 s
- Time to do it
- 5 minutes, plus 2 hours restin
- Difficulty
- Easy
- Steps
- 7
What you need
Steps
Set your multimeter to DC volts. Use the 20V range if it is not auto-ranging, plug the red lead into the V socket and the black lead into COM.
Let the car sit with the engine off for about two hours so the surface charge fades. In a hurry, switch on the headlights for a minute or two to drain it.
Open the bonnet and locate the 12V battery. Most cars keep it in the engine bay, but some models hide it under a seat or in the boot, so check your handbook.
Touch the red probe to the positive terminal and the black probe to the negative terminal. Hold both steady and keep the metal tips from touching each other.
Read the number on the display. A healthy, fully charged battery shows about 12.6 volts or slightly more with the engine off.
Judge the charge from that number. Around 12.4 volts is roughly 75 percent, 12.2 is about half, and near 12.0 or lower means a significantly discharged battery.
Treat the reading as a guide only. A battery can show normal voltage and still fail to crank, so get a proper load test at a parts shop, often for free.
Tips and common mistakes
Wipe dirt and corrosion off the terminals before probing so the contact is clean.
Do not measure straight after driving or charging, because the surface charge gives a falsely high reading.
Wear safety glasses and keep sparks, flames and cigarettes away from the battery, which gives off hydrogen gas.
Cold weather pulls voltage down, so compare readings taken in similar temperatures.
Questions
Can I test the battery with the engine running?
No. With the engine running you are reading the alternator output, usually 13.5 to 14.5 volts, not the resting voltage of the battery.
What voltage means the battery is too low?
Below about 12.0 volts the battery is significantly discharged. Recharge it and test again, and if it drops back quickly it may need replacing.
Do I need to disconnect the battery first?
No. You can test it in the car as long as the engine and all electrical loads are switched off.
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.
