My battery keeps going dead. I had it tested and it is fine - what could be the problem?
Well, your problem could be caused by several things. Let's start with a likely suspect: your alternator. The alternator is like a little electrical generator. It is spun by the serpentine belt on your engine and makes electricity. This electricity is used to power the electrical systems required to run your vehicle. It also powers all your electronic accessories like your stereo, navigation, heated seats, and air fans, as well as charging all the electronics you have plugged in.
After the alternator has done all that, any electricity that's left over is used to charge your battery. You can see where we're going: if the battery isn't getting enough electricity to stay charged the reason may have something to do with the alternator.
Now it could be that the alternator is bad – they do wear out over time. There are several failure points within the alternator, but in practice, it is cheaper to simply replace the alternator than to take it apart and repair it.
Your service center can test your alternator to see if it needs to be replaced. Very often the alternator tests out as being OK - but for some other reason it's not putting out enough electricity to keep the battery charged. Remember we said that the serpentine belt drives the alternator? Well the fault can often lie with the serpentine belt system.
The serpentine belt transfers power from the engine to the alternator. When the belt wears away to a certain point, it is no longer able to provide enough grip and the belt can slip on the alternator pulley so that it is not spinning fast enough to generate all the electricity that your vehicle needs.
A possible related problem is a worn serpentine belt tensioner pulley. This pulley provides tension on the serpentine belt so that it is tight enough to spin the alternator and other accessories. When the belt is too loose, it can slip on the alternator pulley and, once again, not enough electricity is made.
So, when your battery is going dead - test it. If the battery is still good - test the alternator. If the alternator is still good - inspect the serpentine belt and belt tensioner. Chances are good that your service center will get to the root of your problem.
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Fairbanks, AK 99709