How To Tell If Problem Is Car Battery Or Alternator

Don’t you just love those days when the car isn’t starting? You’re thinking that it was running just fine the other day, yet today, nothing. There are many causes that could make a car stall. But here we’re going to talk about the two major components that cause the most trouble: the battery and the alternator. After reading this you should be able know how to tell if the problem comes from your battery or your alternator.

The first thing you will need is a good ol’ fashion voltmeter. That is easily obtainable since you can basically get it from just about any car parts shop. You don’t even need a fancy one. A simple LCD electronic one will do the job nicely. Now the first thing is to determine what is wrong with the car. Simplest of checks is to see if the engine is turning when you turn the key to the start position. If the engine indeed turns but shows other problems, than the car might experience engine related issues, so it should be taken to a mechanic.

If the engine doesn’t budge one bit than you might be dealing with a broken alternator. The battery is the one staring the car, but the alternator operates the car most of the times independent from the battery. The alternator is the one connected to the serpent belt (depending on the car model) and works on the same principle as a bike dynamo. It converts movement into electricity and directs it to the battery charging it while the car is running. One of the most common scenarios of no response from the car is related to the alternator failing. You see, the moment the alternator failed, the battery wasn’t receiving any more “juice” and slowly the battery drained.

Considering that a fully charged battery will function (absent of alternator charging) for just about 30 minutes. If you are using a couple of accessories such as: air conditioning, stereo, lights, or other electrical component, than the battery will deplete faster, shutting down the car completely. In this case your only chance is to replace the alternator. People make the common mistake to confuse a bad alternator with a bad problem. Your best bet is to recharge the battery and let the engine run for a while. If the car shuts off (just like that) then clearly the battery has been drained again, and the alternator needs to be changed.

On the other hand, the battery could be the one causing all the trouble. Ok, that’s what you got the voltmeter for. A battery in perfect condition will have somewhere around 12.66 volts between the + and – terminals. If you see the value drop down below 12V then recharge the battery and check again. If the value is still below 12V then you need to check the battery’s water level, if it’s ok than you may need a replacement.

You should also check the terminals for signs of dirt or corrosion. Passing electricity through the terminals attracts a lot of particles that may form spots of corrosion and greatly affect the battery connectivity. Usually corrosion is easily spotted, but in some cases it may be hidden between the terminals and their connectors. If so, you should use an anti corrosive cleaning agent and a wire brush in order to thoroughly clean up the connectors and the terminal. Afterwards, reconnect the battery and let it charge. If the voltage still drops under 12 volts then you will have no other choice than to replace the battery.