Signs of a bad car battery vs. bad alternator

On the Road 3 min read

The battery is what gives your vehicle the juice the engine needs to crank each day. When the battery starts to go bad, you can easily replace it. On the other hand, a bad alternator fails to properly recharge your battery as the car runs. It’ll cost more to repair than a dead battery if the alternator goes bad. The signs of a bad alternator versus a bad battery are similar, making it difficult to diagnose the exact problem. Knowing the different warning signs of each going bad can help.

Signs you have a bad battery

Almost everyone has had to jump start a car battery at some point, or seen someone do it. Suppose you try to start your car in the morning and it doesn’t turn on. Maybe you left an interior light on all night, causing your battery to die, but it can also mean your battery is going bad.

According to Matthew Hart, owner of AxleWise.com, signs your battery is going bad include:

  • The car is difficult to start.
  • Once started, the car doesn’t hold a charge for very long.
  • Dim or flickering taillights and headlights.
  • Dim interior and dashboard lights.

Car batteries last an average of three to five years, but other factors can shorten their lifespan. If you have additional accessories connected to a car battery, like an internal inverter, it can reduce its overall lifespan. If you notice issues with your car, look at the battery itself. According to Patrick McCann from WeTryTires.com, “There may be corrosion around the points on the battery.” This corrosion can be a sign of degradation, but the battery may also need a cleaning. Your vehicle might also have a warning light indicator on your dashboard if your battery is beginning to give out.

Signs you have a bad alternator

Your car’s battery holds a charge, but the alternator works to recharge it while the vehicle is on. That’s why you can drive all day long without a problem but leaving the lights on overnight will drain the battery. If the alternator begins to fail, the battery will no longer recharge while the engine is running.

Here’s how to tell if your alternator is bad. One of the most obvious signs is if the car dies after a jump start. The alternator should provide enough current to keep the vehicle running even with a bad battery. If it doesn’t, then your alternator needs to be examined.

According to Matthew Hart, “If your alternator is going bad, you might see the voltage meter on your dashboard start to drop, or your car might start to vibrate while you’re driving.” The vibrations are typically caused by misfires within the spark plug caused by a lack of current from the alternator.

Another way to know if you have a bad alternator, according to McCann, is by checking the battery voltage after charging it up. “If the [battery’s] voltage is low, replace with a new battery or charge the battery to the recommended 14.2 to 14.7 volts,” he says. “Then try to run the vehicle and see if the voltage after is outside of that range. If it is, that’s a sign of a bad alternator.”

How to fix a bad battery or alternator

If you have a bad battery, you can purchase a new one from almost any auto parts store. Many stores will replace the battery as part of the purchase cost. You can also replace it yourself if you know how to do it. Do your research to find the best battery for your needs. An alternator may cost more to repair than to replace the battery. The price you pay will depend on the make and model of your car and the parts and labor costs.

If your battery or alternator goes out, you should take your vehicle to a mechanic and have it inspected. While the signs of a bad car battery versus an alternator can be obvious, they can also point to other, more subtle mechanical problems.

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