How to check your cars battery with a Digital Multimeter #FCDDIY#004
Overview:
Duration: <5 minutes
Difficulty: easy
Cost: free if you have a digital multimeter, if you don’t they cost around €10-20
Type of DIY: nice to know, saves time (you can leave the battery in place), can save your battery’s life!
Let me start with what you need for this DIY:
- A car (obviously) that has a 12V battery (most passenger cars have 12V batteries)
- A digital Multimeter (+ the cables that come with it)
Setup
#1. Plug in your cables correctly, the user manual of the DMM helps you with that
#2. Choose “20” within the “V” (for Volt) part of your DMM —-> 20V means you can measure up anything to 20 Volt (12V in this case)
Now connect your DMM to your battery, without the car running!
If you connect the black cable (-) to your (+) terminal you'll see this: 12,72 Volt
If you connect the red cable (+) to your (+) terminal you'll see this: -12,71 Volt
Now what do these numbers mean you ask?
From several internet forums I’ve gathered the following information:
Quick overview:
Voltage should be between 12,4V and 12,7V.
If it’s below 12,4V charge your battery.
Detailed:
12,65 Volt: fully charged
12,5 Volt: average charge (85%) ()
12,3 Volt: weak (or half empty = 50% )
11,9 Volt: discharged (immediately charge your battery!)
10,7 Volt: exhausted (broken, can’t be charged again with a normal charger)
Additonal information:
With your engine running and under the load of your headlights etc. the Voltage shouldn’t sink under 13,8V, a minimum 14,1V would be ideal.At or below 13,8V means you should immediately charge this battery.
You can also start up your car and then check the Voltage again!
Mine reads, 14,42V with the engine running under load (headlights, etc.)
My car battery as a living example:
I charged my battery a few weeks ago so it should be good right?
Condition with the engine turned off:
12,72V is very good, a bit above an average fully charged battery.
Condition with the engine turned on:
14,42V well above the minimum of 14,1V so that seems very good too.
Fortunately it seems as everything is fine.
Pro Tip: if your battery has a voltage of less than 10,7V without the engine running, you don’t have to throw it away!
Buy a CTEK MXS 5.0 or a similar charger that offers a RECOND function, with this function you can save the life of an exhausted battery! Cheap charges sadly won’t help at this point.
So charge your battery before it gets that low!
Tip: Charge your battery before winter or every so often if you do alot of short trips!
Thank you for reading through, I hope this helped you, leave me a comment with your feedback if you want to :D
And feel free to ask any questions!
Yours sincerely,
First_car_Dacia
Comments
Something wrong? Or am I reading it wrong?
Thank you for pointing it out, fixed that!
Uuuh dude, your multimeter is hooked up wrong..
Black probe is COM
Also, if while your car is running and you get below 14, its not your battery’s fault, its the alternator going bad.
“Ignore the “-“ infront of the Volt, that’s just because you connected it the wrong way but it doesn’t matter”
Ah interesting, well you learn something new every day :D thanks
also check one of #ChrisFix brilliant Videos: https://www.youtube.com/watch?v=LGB6ZEjGm7Q
Thank you, awesome video!
The method here is solid, but there’s a little bit of mis-info. What you’re checking here is the battery’s voltage, when what you really want to be checking is amps. It’s very possible for a battery to rest at 12.7 volts and still not have enough amperage to turn the car over, hence it would be a bad battery. There are two common ways to test for amperage, either by putting an analogue load on the battery to simulate starter draw, or to use a digital load tester which measures resistance between cells to simulate amperage output. If calibrated correctly, an analogue meter will be more accurate.
Testing battery voltage with a multi-meter is more of a way to make sure that your alternator has been charging your battery, although you can derive a little bit of info from checking battery resting voltage over amounts of time, but other factors such as temperature and (believe it or not) the amount of dirt on top of your battery can also contribute to atmospheric discharge rates.
Seriously, dirt is very slightly conductive and if your battery is dirty it’ll discharge faster. You learn a lot when you work in a battery store for years lol
Thank you for the input!
I am aware of the fact that a certain Voltage doesn’t necessarily mean the battery is good, but I like this simple method to gather atleast some information :)
But I know you understand me.
This is definitely good to know.
Good :)
I just check for voltage before during and after running, usually points in the right direction of the fault. If its charging and showing good voltage and not starting properly usually bad contacts. If that dont fix it then amps is the problem. Most people wont have a proper amp or cca tester etc and ive never need to use one. (I work on heavy plant but all the same stuff)