Bad Battery vs. Bad Alternator

Christopher John

Because the alternator and the battery are both components of an automobile's charging system, the operation of one affects the other. If either of these parts is bad, you can diagnose which one it is by knowing and identifying the specific signs that each of the bad parts will give.

A bad battery and a bad alternator will each give out signals.

Bad Battery Signs

replacing a car battery

The easiest way to know you have a bad battery is when the battery light illuminates on the dashboard while you are driving. The sign of a dead battery is obvious when you get in a vehicle, insert the key in the ignition and turn the key. You will hear nothing at all when the battery is dead. If the battery is bad but is in danger of going dead, you will hear a clicking sound when you turn the key. Also, conduct a visual test of the battery under the hood, looking for corroded leads or split wires, which can indicate a bad battery.

Bad Alternator Signs

replacing an alternator

Outside of spotting an illuminated dashboard light indicating a problem with your automobile's charging system, you can diagnose a bad alternator in other ways. If the automobile won't start, turn on the headlights. If the headlights shine brightly, that can be the first indication of a bad alternator. Next, turn the key in the ignition to try starting the car. If the lights continue shining bright while you do this, but the automobile won't start, the problem is likely a bad alternator. If you are driving with the headlights on and the lights dim when you slow down, this also indicates a bad alternator.

Bad Alternator and Bad Battery Effects

A bad alternator will not charge your battery

Depending on how much electricity an automobile requires, it can run for a short time if it has a bad alternator. The alternator's job is to recharge the battery while you're driving once the battery has started the car. A bad alternator will not properly charge the battery. Also, if the battery itself is bad, an alternator in working order won't be able to charge it.


Replacing an alternator is not hard.

When you replace a bad alternator, you can install a rebuilt alternator in the automobile that will work as well as a new alternator. Because the alternator is usually located in an accessible spot on top of the engine, it is normally a light task. A properly working alternator can often recharge a dead battery by running the automobile for a period of time. You can also charge up a dead battery with a battery charger. When you change out a bad battery, be sure to obtain a replacement that has the cold cranking amps that your auto needs.