Car Battery Testing

One of the services that we offer is battery replacement and testing, but before you call us out to get a new battery fitted, it makes sense to check that the battery really is dead. It’s also a good idea to test your batteries periodically anyway, so that you can get an ‘early warning’ that the battery is losing power and replace it before the winter kicks in.

How to test a car battery at home

You can test your car battery at home with a voltmeter or a digital multimeter. This equipment is quite easy to use, and it is not expensive either. These tests will tell you whether your car is producing sufficient power, and how well charged it is. These tests are quite simple, and involve attaching a DC-reading multimeter to the terminals on the battery, and reading the level of charge.

It’s also worth testing the health of the cells, and paying for a load test if your battery is a few years old. These home tests will not solve or diagnose every problem that there could possibly be with a car battery, but they are a useful starting point, and they will give you an idea of whether your car battery simply needs a recharge, or whether there is a more serious issue.

How to test a car battery with a voltmeter

If you think that your battery has some problems, then you can do a full test with a voltmeter. The result of these tests will help your mechanic or the battery manufacturer tell you what the problem is with your car’s battery. To test a car battery with a voltmeter, stop the vehicle and turn off the power. Disconnect the battery from the engine, removing all the cables attached to it. Clean the terminals, take a reference reading, and make a note of it.

Charge the battery for a full charging cycle, then let is sit for 30 minutes or so, before taking another reading. Next, let it sit for 12 hours without being used (do not load the battery at all), and test it again. Make a note of the third reading.

Finally, hook the battery up to the vehicle and connect the volt meter, and attempt to start the car. Make a note of what voltage the battery drops to.

How to test your car battery with a digital multimeter

To test a car battery with a multimeter:

  • Set the multimeter to measure DC voltage
  • Set the meter to 20 volts
  • Turn the car off
  • Disconnect the battery cables
  • Attach the multimeter to the battery – one lead goes on the positive post, the other on the negative - the leads will be labelled to show which does on each terminal.

If the battery reads 12.66v, then this means that it is fully charged. 12.45v means that it is 75 percent charged, 12.24v means that it is half charged. If the reading drops below 12v, then this means that the battery is at zero or close to zero charge.

These figures assume that you are taking the readings at 80 degrees F. At colder temperatures, the battery will show slightly lower voltages at full charge. For example, at zero degrees F, a 12 volt battery will show 12.516v when it is fully charged.

What is a load test on a car battery?

A load test shows the amount of power that the battery is capable of putting out over a sustained period, when it is tested under one half of the CCA rating, at a temperature of 70 degrees Fahrenheit. The test should not be done using a hand-held tester, but rather with a true load. The battery should be fully charged before the test to get an accurate reading. You should take your car to a mechanic or a store with battery testing facilities to get a proper load test done.

Make sure that the test that they carry out is a ‘Carbon pile’ test. Some mechanics try to pass off specific gravity or conductance tests as being load tests, but these are not quite the same thing. The carbon pile test will give you the best idea of the useful life of your battery.

My car battery failed load test

If your battery failed the load test, it’s well worth getting a new one as soon as possible. Batteries only have a lifespan of a few years (exactly how long depending on the climate, and your car usage patterns). Once a battery starts to degrade, it’s only a matter of time before it will give out, and you could find yourself stuck waiting for someone to come out to start your car. It’s far more expensive to get rescued then replace your battery, compared to having it replaced early on. In addition, a weak or damaged battery could be placing unnecessary load on your alternator, and replacing a damaged alternator is an expensive job too.

Car batteries are sensitive pieces of equipment. They lose charge over time, and if the cells become stratified or the batteries freeze in cold weather then this will render the battery unusable. Do not try to operate a car with a battery that is seriously damaged. If your battery is showing signs of leaking, is warped, or the cells have started to swell, then you should not even try to recharge it.

If the battery is still intact, remove it from your vehicle and ask for advice. If it is physically damaged, call a car repair service and ask them to safely remove the battery for you. Battery acid is highly dangerous to the environment, and to people. It could burn your skin, and could cause blindness if it gets in your eyes. For this reason, batteries should always be handled with care. When a battery is disconnected from your car, you should always keep it on a flat, stable surface, out of reach of pets and children.

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