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How To Tell If Its A Car Battery Or Alternator Problem

Electrical problems are some of the most complex problems the car may have and can be the source of the widest array of symptoms and car behaviors. Yet with a little bit of will anyone can, if not master, at least know the difference between a car battery and a car alternator and what they do and imply. First of all the car battery is the “heart” of the entire electrical system. It stores energy and is used to power up all the devices and features the car has (headlights, windows, mirrors, air conditioning, CD player etc.). The alternator is the one that charges up the battery when the engine is running, converting motion provided by the engine into electricity.

So let’s begin with the battery. It can be tested in a number of ways and may give you certain symptoms from which you can detect if it’s faulty.

How To Tell If Its A Car Battery Or Alternator Problem

The first step is to test the voltage of the battery with an electronic multimeter. A new battery in perfect shape will develop 12.66 volts between the + and – terminals. The number may vary from this value in case the car is bigger or smaller, but no less than under 12 volts or over 13. In case it is fully charged and still displaying under 12 volts it means that it’s slowly deteriorating and it may need replacing.

If your battery is ok and still the engine won’t start than you need to check the terminals. The problem may be a simple connection problem which can be easily fixed. Or just a bit more complicated, and may require cleaning the terminals in case of corrosion. Still very manageable, cloth and anti corrosive agent is all you’ll need to make the terminals shiny. If the terminals are corroded or simply dirty, it means that a proper connection is not formed and it may lead to faulty charging and less power to the car.

The last thing you can do. Is perform a load test. Place the tester between the two terminals and let the battery charge. If the charging is complete and still the battery fails the loading test than it may need replacing.

If you’ve done all that than the battery is ok and can be eliminated from the equation.  It’s time to switch to the alternator. This is the battery charger and without it, the battery will drain so the car won’t even start. The simplest test is to check the alternator dashboard indicator. If it turns on than the alternator is functional, if not than there may be a problem.

Check the connection belts because the alternator may be developing low output in case the belts are worn out or too loose. In both cases, the engine will not transmit the rotation properly to the alternator and this preventing the alternator to create enough energy to power up the battery, meaning low power and a lot of headaches in the morning when the car won’t start. Corrosion, or dirty terminals may also be the cause of poor battery charge.

You can inspect the battery voltage and connections while the engine is on idle. Use a digital voltmeter to check out the connections. If the output is between 13.8 - 15V. In case the reading drops under 12.8 V than the alternator is not developing as much electricity as it should.

The last option is to listen for some weird grinding noises coming from the alternator. It may mean that the rotor may be failing within the alternator. If that’s the case than take it to a specialist.

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