A battery is an essential component in the operation of a motor vehicle, and they have a tendency to fail at the most inopportune of times. The good news is you can work out precisely what the problem is by performing a few simple tests on the battery with a voltage meter.
12.6 volts is the number that a healthy car battery should be registering. It is important that the battery be tested around an hour after the car was last used in order to read the resting voltage, as a higher reading is likely to be given if the car has recently been driven and can be misleading.
The best advice is to leave the vehicle overnight before testing the battery so as to ensure the accuracy of the charge state.
It is easy to use a voltage meter to test a car battery. Make certain that the battery terminals – those metal connections on the battery’s front or top – can be accessed.
Car batteries are usually found in the engine bay to the side of the engine. If you cannot immediately see the battery when the bonnet of the car is opened, have a look in the owner’s manual. Batteries often come with plastic covers in modern vehicles and may need to be unclipped, hinged up or sometimes even removed with a couple of screws and bolts.
After the battery has been exposed extreme care is required to ensure that nothing metal comes into contact with the terminals, as this could cause a short.
Using a voltage meter to check a car battery
The first test with a voltage meter should be to measure DC voltage, which is indicated with the presence of a solid line as well as a dashed line over the letter V. The dial should be set to 20 to allow for an accurate measurement from 0-20 volts.
The red probe should be touched to the positive terminal (which is normally also red) with the black robe touching the negative terminal (which is normally also black). Terminals are differentiated with the + and – symbols. A reading with a minus figure is an indication that the probes are the wrong way around.
A resting voltage should have a rating of no less 12.6V, with a battery reading 12.2V actually only being charged to 50% capacity and below 12V will be classified as being discharged.
“Parasitic loss” is a phenomenon experienced by all modern vehicles referring to when the battery is drained by something electrical even when the engine is not on. Alarm, clock and computer systems still use some power and if this seems to be killing your battery while your car is in storage, it might be an idea to remove or disconnect the battery for the duration.
A voltage meter with a reading of less than 12.6V should be disconnected and then fully charged via a battery charger and then allowed to rest overnight. If a charge is still being held when disconnected from the vehicle, something else is quickly draining the battery.
A simple test with a voltage meter is the best way to check whether or not your car battery is working properly.
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