Troubleshooting: Is It a Bad Alternator or Battery?

Signs of a bad alternator or battery — What to look for

One of the most obvious signs of a bad alternator or battery is trouble starting your car. If you turn the key and hear nothing or just a clicking sound, your battery probably isn’t charged enough to fully engage the starter. A failing alternator may no longer be charging your battery sufficiently while driving.

There are other signs as well like:

• Dimming or pulsating headlights or dash lights while idling or driving, especially at night.
• Strange smells or sounds can also signal problems.
• Electrical components like power windows, locks, or stereo acting sluggishly or intermittently.
• The check engine light may activate due to voltage irregularities.
• Phone chargers and accessories connected through USB ports may stop functioning since the battery can no longer provide sufficient consistent power.

How to determine whether the problem is a bad alternator or battery

It all starts with the battery because an alternator can’t produce power unless it has power. So disconnect the battery cables and connect a battery charger. Once the battery is charged, get it tested at any auto parts store. If it tests good, then perform an alternator test. See this post on how to test an alternator. If the test shows it’s bad, replace it.

An alternator can also have mechanical signs of a failure

An alternator rebuild kit usually contains a new voltage regulator (if needed), a new front and rear bearing and a new brush set (not shown).

Alternators contain two bearings, a brush set and an over-riding clutch. When those parts wear, they create growling or squealing noises; signs of a bad alternator.

Use an automotive stethoscope to check the sound of the front and rear alternator bearings. If you hear growling or one bearing is considerably louder than the other, chances are one of the bearings is failing.

©, 2022 Rick Muscoplat