hey whats up youtube welcome to another video by ratchets and wrenches and today I am going
to show you how you can test your car battery using a multimeter.
ok but before we get onto the testing procedure which should only take a minute or two lets
quickly go over what are some symptoms of a bad battery and also what are some common
mistakes people make when they are trying to figure out a problem with their car’s starting
Ok so the first mistake people usually make is that they misdiagnose a bad battery with
a problem with their starter, that happens usually when they go one day to start the
car, they turn the key and all they hear is a ticking sound, or they turn the key and
the car turns over very slowly and it doesn’t start, or in other cases they put the key
in the ignition they have power when they put the key in the ignition but when they
turn it they hear a loud pop and than there is no power at all.
In those first two instances people usually think that there is a problem with their starter
and since the car is only turning over slowly, its draining the battery but if you have a
good battery you should be able to crank the engine for 30 seconds without any hickups.
So that actually means your battery is weak and its not supplying enough amps to your
starter to turn the car over fast enough for it to start.
But in the third example, in my experience thats usually indicates a problem with your
battery terminal connectors, they’ve either become loose or they are damaged there’s also
the possibility of excessive corrosion build up around your battery terminals and your
battery terminals connectors so you need to inspect those and if they are dirty to clean
Dirty battery terminal connectors are the number one cause of your battery dying.
Second most common mistake people make is that they mistake a battery problem with a
problem with their alternator.
What happens in those instances is that one day they go to start the car, they can’t start
it so they get a jump start the car starts fine and runs fine but as soon as they start
driving around and you know once they start using their accessories maybe roll up a window,
turn on the ac or even step on the brakes the car shuts off.
Now its common knowledge and also true that the battery is only there to start the engine
once the engine starts the alternator takes over and supplies power to the car.
But what happens there is that your battery is completely shot and you probably have heavily
corroded battery terminals and battery terminal connectors and that puts and extra strain
on your alternator and your alternator is not able to deal with that and therefore once
you start using more accessories in addition to that extra strain your car shuts off.
Also it should be said if you don’t replace a weak battery or a battery thats going bad
that extra strain on your alternator it could cause your alternator to go bad as well.
Ok now onto the actual testing procedure, what you’ll need to do is to get your multimeter,
turn it on and than turn the setting to DC Voltage, on this multimeter it only says V
but on most multimeter’s you are going to see DC V which stands for DC Voltage and the
setting you want on that is for 20. and also these multimeter’s are really cheap you know
you can get a even a simpler version of this at harbor freight for under 10 bucks.
what you want to do next is to touch the negative side of the battery with your black lead and
the positive side of the battery with your red lead.
And the voltage reading you are looking for is about 12.4 to 12.8 volts.
Now I am going to be using these clamps to hold these in for this video but you obviously
don’t have to you just need to tough them.
And there you have it we got 12.7 Volts.
Ok so the voltage reading is within spec but in order to be sure that our car battery is
indeed good, we also need to do a load test on the battery.
Now there is testing equipment that put a load on the battery and than measure how the
health of the battery but we don’t have that so what we are going to do is actually start
the engine therefore putting a load on the battery and than measure our voltage drop,
we don’t want to see the voltage drop below 10.5 Volts.
If the voltage drops below 10.5 Volts there is a chance that there is a problem with your
battery it could need to be recharged or it could be bad, Ok so as you might have seen
our lowest voltage drop was at 10.6 volts and that’s within spec therefore we’ve verified
that this battery is indeed good.
Now those were obviously good numbers and I knew this battery was good before I started
this video but lets talk about different numbers, lets say on the voltage reading you get 9.5
volts or lower.
Anything in that range, you pretty much need to replace your battery, umm your battery
is done for there is no charging it, there’s nothing you can do you just need to replace
But lets say you get 11 volts, at 11 volts there is a chance you can recharge that battery
and what I would do is you know if you have corrosion on your battery terminals or your
battery terminal connectors are damaged or loose I would replace them thoroughly clean
them, than put them back on the battery if you can start the car or get a jump start
get the car going, and get it to a local auto parts store and they’ll be able to put a load
test on your battery and determine whether that battery can be charged or still needs
to be replaced.
Now lets say you replace your battery and get a brand new battery put it in the car,
you change your battery terminal connectors or clean the thoroughly but than again the
next day you go to start the car and you still can’t start the car.
Well that usually means there is a parasitic draw on your car’s battery, and its emptying
out the charge in your battery and we’ll need to find it.
I’ll do a follow up video covering that and than after that I’ll do a video on how to
test your alternator using a multimeter as well, OK so yea hope this video helps people
out there, if you liked the video please give it a thumbs up subscribe if you want to see
more like it and I’ll see you next time.
Thanks for watching.