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How Automobiles Work


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 system. 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 them thoroughly. 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 it. 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.

43 thoughts on “How to Test a Car Battery – Plus Tips on How to Prevent a Battery From Going Bad

  1. It always surprises my how often people get this wrong. Even professionals sometimes forget to check the engine ground connection, and overall the diagnostics are not as easy as some people think. Your review is exactly right, especially the emphasis on load testing. Also it's worth emphasizing that a battery needs to be warm, electrolyte level is normal, and fully charged before before testing. I find doing the load test away from the vehicle avoids the confusion about bad connections, so your remarks about double checking the battery at a local store is great advice. 

  2. Thank you for the informative videos.  Can anyone please help.  My battery voltage is 12.67v and when i start the engine the voltage does not seem to change.  When I checked the voltage from the leads without being connected to the battery it was over 18v.  Is this a bad Rectifier/ Regulaor on the alternator.  Could a fuse be blown.  So battery does not seem to charge.  I cannot start the engine using the ignition key.  I have a 25hp mariner efi cdi elpt.  The tilt switch is also totally non responsive.  I have come accross people with a similar problem who changed a fuse and problem solved.  But where do I find the fuse.  I can start the engine no problem with the pull cord on the flywheel and engine runs without a hitch.

  3. Good stuff, easy to understand "gracias".I'm going to test my battery tomorrow.The central locking is not working ,there are no lights on the dash? Not sure what's happened,but the ignition fuse was blow,replaced that,but still no life? C'est la vie I guess

  4. Very explanatory…. Great video… Thumbs up for sure… Appreciate the time and effort… Very informative…Keep'em coming..

  5. the best success that ive ever had was with the Magic Mender Wizard (just google it) without a doubt the most incredible info that I've tried.

  6. you said if it goes 9.5 or below you need a new battery but if it reads 11 you could charge it…..did you mean to say 10?

  7. used touch screen for too long and "powering off to save battery" popped
    up. checked voltage and it's 12.1. wont' be driving for awhile, maybe
    a week will it start later?

  8. Ratchets and Wrenches, can a car electrical system run from the alternator after the car is started and the battery is dead?

  9. My car battery was sitting for about 2 months in low temps -2 to 5 C and it wouldn't start the car. I charged it drove it and it then sat again for a good 2 months in temps around 5 to 11 C, I didn't start it but checked the voltage which showed 12.4. My charger was giving 2 amps which increased to 3. Also if you have a bmw you can check volts on the dash by holding the trip reset until it flashes yes/no, select yes go to 19 then 9 (E46)

  10. Really appreciate all of your video's. You're definitely my goto guy on electrical issues. You're very thorough, and I write down everything. Will be tackling a electrical drop on voltage and amps soon with my little airplane. All of your video's give me confidence to hopefully get to the bottom of it. Thanks!

  11. My battery read 12.6 with engine off a soon i turn on the headlights read 11.10 so is this posible bad battery .? But if i started the engine from 12.6 i got 14.3 so what is the problem battery or alternator .?

  12. I was just about buy a new battery for my can but was able to use your guide to quickly recondition my old battery instead! I was not expecting it to be that easy [Check Details Here==>http://bit.ly/BatterySecretGuide ]. That already save me over $100 and there are so many other batteries I am going to recondition with your course now too! Thank you.

  13. The voltage on my car's battery reads 12.3 when connected and 12.6 when terminals disconnected. Is this normal? What could cause this?

  14. New battery,multimeter shows 10.4 when cranking and min/max function on multimeter shows a min of 9.7 v.All ok and cranks fast.Info you provided is not valid.

  15. can removing a parking light bulb in the front of 03 silverado cause batery to go ded? its exactly wat i did took the bulb off 8hrs later the batery was ded wat the ef?

  16. My battery froze. I live in ct. I didn’t start the car for two weeks. Can I put it inside my house to thaw it? Thanks in advance
    Also what’s the best recommendation for a car battery if I’m not gonna use it for three months? So when I come back it’s not dead

  17. Forgot tomention that a bad starter can cause a voltage drop that exceeds 10.5v when cranking. But he would have caught that on a more thorough battery test. If you need this video to check your car dont. Take it to a professional.

  18. So they will make a truck… That's good. For some time now I've been figuring "If Tesla really wants to make money, they'll make a viable ( lovy.biz/44oi )1/2-ton LUV fleet-truck.". And they plan to make Class-8 semi-tractors & buses as well? Makes me look forward to the first luxury EV motor-home, built with fixed roof-top & retractable solar panels, all powering the EM-induction cook-top, water-heater & washer/clothes-dryer. Add a water collection system with reverse-osmosis treatment & UV-sterilizing, and you'll be set to survive anywhere, anytime!

  19. Excellent instruction on how to evaluate a car battery. Now I understand what to do and what to look for. So, even though one of my cars is showing 12.3V, with a load, the output is not sufficient.

  20. Sir, please kindly take take note on the question below…
    Say, the battery is showing 12.7 volt on checking multimeter, however, checking gravity tests on each cell, if anyone shows reading out of range, should I confirm the battery is going bad???
    Which is the best and correct to identify battery is dead and needs new battery??? Voltage reading or gravity tests????
    Thanks.

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