Here is how you check your car battery

How to perform a Car Battery Test

17 March 2015, 15:17

There is nothing more annoying than going out to your car in the morning and finding that the battery has gone flat and the car won’t start. It can ruin your plans for days whilst you work out alternative transport arrangements and get any potential maintenance problems fixed. Keeping an eye on your battery and regularly checking its performance is the best way to avoid this from happening.

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How to test your battery

Testing your car battery on a regular basis couldn’t be easier with the help of a car battery tester. The first test you will need to carry out on your battery is to determine how much charge it has. To get the most accurate results of your battery’s performance you should wait 12 hours after having switched off your engine to test the charge level. This will allow enough time for any surface charge to run down and if your battery has problems retaining charge then it will be easier to spot if you wait a bit.

  • Ensure that the engine is not running and open the car bonnet.
  • You may want to put on gloves to protect your skin from any possible acid leaks.
  • Remove the car battery tester from its packaging and find the instructions for use.
  • You can test your car battery without having to disconnect it from the car. Just make sure that you have easy access to it in order to correctly connect the wires.
  • Follow the instructions on your car battery tester to connect the terminals to the correct points on the car battery. You should connect the red lead to the positive (+) terminal on the battery and the black lead to the negative (-) one
  • Press the button to start the test.
  • You should be aware that at colder temperatures, the readings will be lower. All of the figures given below are for batteries tested at 21°c. If it is colder than this when you test your battery then you can expect slightly lower readings, which will not be a reflection on the performance of your battery.
  • After a short while you should get a numerical reading come up on the screen of your car battery tester. The reading will correspond to the voltage stored in the battery, and how much energy it has retained over 12 hours will tell you a lot about the state of the battery itself.If your car has a standard Sb/Sb 12V battery, a reading of 12.65V will mean that the battery is fully charged. 11.89V will mean that the battery is completely flat. The closer the reading is to 12.65V the better. If your car has a maintenance free Ca/Ca or a VRLA 12V battery, a reading of 12.77V corresponds to a fully charged battery and a reading of 11.75V will mean that it is completely dead.

The second test you can perform on your battery is to measure its level of sulphuric acid with a hydrometer. This is only necessary if your battery is non-sealed. If you buy a hydrometer, it will come with exact instructions as to how to measure the concentration of the acid and what the readings mean. Some newer cars will have an in-built hydrometer on the battery itself which uses colours to indicate the acid level. Green is for good condition, yellow is if the battery needs charging or maintenance and red for when the battery should be replaced.

What if the test fails?

If the test fails then you will need to replace your battery.

Can you replace the battery yourself?

Changing your car battery is not an overly complicated procedure. It is perfectly possible to do it yourself, but you will need to be very careful if the old battery is damaged in any way. The acid inside the battery is highly corrosive and it can be extremely dangerous if not handled correctly; so you should wear gloves at all times to protect your skin. It is also much easier than you might think to connect the wires to the wrong terminals and short circuit the electrical system of the whole car. If you have any doubts whatsoever about the process of replacing the car battery then you should leave it to a professional.

Car batteries can’t be taken to landfill sites without having undergone a rigorous treatment process first. If you do decide to change the battery yourself then you will be left with the problem of what to do with the old battery. Most garages will know where you can take the car battery but may be unwilling to take it off your hands if they have not been the ones to replace it for you. Alternatively, many large chain stores that specialise in selling car parts and accessories will have facilities to properly dispose of car batteries safely.

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