Can You Jumpstart a Car With a Bad Alternator?

If you have a car and you’ve experienced the infamous “​won’t start”​ situation, you know how truly stressful it is. Jumping your car is one of the easiest ways to get it started again.

With a dead battery, you will need to jumpstart the vehicle by connecting another live battery to the car. But what if you have a bad alternator? Can you jumpstart a car with a bad alternator too?

Can you jumpstart a car with a bad alternator?

Yes, you can jumpstart a car with a bad alternator. The problem is that it won’t get very far. A dead or low voltage battery will not be able to supply enough current to run the starter motor, so you will need to charge the dead battery for as long as possible before disconnecting the cables.

If you have a fully charged high-capacity battery, it should last from 30 minutes to one hour if driven in daylight hours and no accessories are used (no radio or lights). The battery has to be healthy enough to power everything for that long. If it is old and worn out, then it might fail after just a few minutes.

Turn off every electrical load you can before disconnecting the cables to conserve power. This includes lights, radio, accessories like power windows, etc., and anything else drawing power from your battery.

If you are planning to go on a road trip, here’s a guide from USA Today on how you can get road assistance in case your alternator or battery goes bad.

How do you tell if it’s your alternator or your battery?

Both a dead battery and an alternator that isn’t charging can cause similar symptoms, so it’s important to know how to tell the difference between them.

Bad Battery

If you’ve got a dead or low battery, the charging system warning light will be illuminated on your dashboard. Here are some simple checks you can do at home to see if it will start and run.

  • The first thing to do is check the battery terminals for corrosion. If you see any, it means that the battery is old and damaged, so you should replace it.
  • Next, try to jumpstart your vehicle. If that works, then you know you have a battery problem.
  • The easiest way to check your battery’s charge level is by using a multimeter or voltage tester.
  • Simply attach the leads from the multimeter to each terminal on your battery. The reading should be between 12 and 14 volts for most cars.
  • If your reading is lower than 10 volts, then it’s time to replace the battery.

A failing alternator can also cause a dead or low battery because it will draw too much power from your battery and leave it drained and unable to start up again until charged.

Bad Alternator

  • If it’s the alternator, it may be harder for you to start your vehicle at first, but once it gets going, it should continue running even with no power from its alternator.
  • Just like the battery, you can also test your alternator using a multimeter
  • First, you have to set your multimeter to DCV (DC Volts) above 15. Make sure both of your alternator’s terminals are clean.
  • Put the multimeter’s black cable to the negative terminal and the red cable to the positive terminal. The ideal alternator reading should be around 12.6.

We highly recommend ANCEL PB100 Automotive Power Circuit Probe Tester, 12V 24V Car Electrical Test Tool Kit AC DC Current Resistance Short Finder, Multimeter, Digital Voltage Meter, and Test Light Diagnostic which you can buy on Amazon.

Alternatively, you can also test your alternator without a multimeter.

How do I charge a car battery with a bad alternator?

The alternator is a crucial part of a vehicle’s operation. It helps keep the battery running by charging it with energy when the engine is running.

If you decide to jumpstart your vehicle with a bad alternator, be aware that it will take much longer than usual for your vehicle’s charging system to replenish the battery’s charge. You may have to wait for hours before you can drive again. You can charge a car battery with a bad alternator using the following:

Jumpstart the car

If your battery is completely dead (empty), then you’ll need a jump start. This involves connecting another car’s battery to yours with jumper cables and starting the car.

This sends electricity from the good battery into yours, which should start up again once the engine starts turning over.

Read more: Jumper Cables Melted – Top 3 Reasons Why

Connect to car battery booster pack

A car battery booster pack, like the NOCO Boost Plus, is a portable jump starter box that can be used to jump-start cars, trucks, motorcycles, and other vehicles. They are also called Car Battery Booster Pack, and Portable Power Bank Charger.

Check Price on Amazon

They are designed to safely connect to any 12-volt automotive car battery and allow the user to start their vehicle or motorcycle.

Connect to a trickle charger

Another popular type of car battery charger is known as a trickle charger. This type of charger works by slowly charging your vehicle’s battery over an extended period (usually between 12 and 24 hours).

The advantage of this method is that it ensures that your battery receives an even charge without being overcharged or damaged by excess current flow. However, trickle chargers do not provide enough power to jump-start a dead battery.

How long will a battery last with a bad alternator?

If you have a bad alternator, the car will depend on the health of the battery. The battery is constantly being drained. Depending on the battery, you can drive from 30 minutes to 1 hour before the battery goes dead.

Turn off other electrical components such as lights, AC, and radio while driving. This will help preserve your battery life. Drive to get home or drive to the nearest auto center for assistance.

Drive the car to get home or drive to the nearest auto center if possible.

Read more: How Long Do Car Batteries Last? It Depends on Many Factors

Risks of driving with a bad alternator

Driving with a bad alternator can be quite dangerous. Alternators are responsible for charging your car’s battery, providing power to run essential electrical components like lights and air conditioning.

According to The Drive, alternators last around 6-10 years or roughly 80,000-150,000 miles. your alternator is damaged or broken, you may experience several symptoms that indicate a problem:

  • Your car won’t start. The battery may not have enough juice to get the engine going, especially if it’s older than five years old and has been subjected to heavy use.
  • Your lights flicker or dim when you start the engine. The alternator is responsible for powering the headlight bulbs and keeping them bright, so this is one of the most common signs that something is wrong with your alternator system.
  • Your AC doesn’t work properly. If you have an older vehicle with manual controls, you may notice that your air conditioning isn’t cooling as well as it used to when it was new. This could be caused by an alternator that isn’t providing enough power to run all of those electronics in addition to charging up your battery.


You can jumpstart a car with a bad alternator. The question is: will it get you very far? If your battery is completely dead, then no amount of cranking will give you enough voltage to run the starter for long.

car with a bad alternator will frequently have a dead battery, so keeping an eye on your battery’s health is key. So, one way to keep a car running for longer would be to charge the battery as much as possible before disconnecting the cables.

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