Will an Alternator Charge a Dead Battery?

If you’ve ever wondered whether an alternator will charge a dead battery, the answer is: it depends.

If your battery is totally dead, meaning that it won’t even turn over and you can’t start the car, then no—your alternator won’t be able to charge your battery.

If it’s just drained of energy or drained because you’ve been using a lot of electricity (for example, if you’ve been running a bunch of lights or something), then yes! Your alternator can probably get things going again.

The reason why it depends on how much power is left in your battery is because the alternator works by taking energy from the engine and transforming it into electricity for your car’s electrical system to use.

The more electricity that has been used up by other parts of your car’s electrical system, the less there will be left over for charging purposes.

How long will an alternator charge a dead battery?

Well, that depends on how much energy was stored in the battery when you started charging it with the alternator.

If your battery was completely drained before starting charging, then your alternator will probably be able to fully recharge it in about 20 minutes or so.

But if there is still some charge left in the battery (and most cars have at least some), then your alternator may take longer than 20 minutes to get all of that juice out and back into your car’s electrical system again!

Factors that affect charging time for a dead battery?

The amount of time it takes to fully charge a drained battery depends on the size and condition of the battery, as well as how much current your alternator can produce.

The size and condition of your battery will determine how much power you can draw from it. Therefore, if you have a new battery that’s in good condition and is fully charged, then it should only take about 15 minutes for your alternator to fully charge the battery.

If you have an older, worn-out battery or one that’s low on fluid, then it may take longer for the alternator to charge it.

The amount of current your alternator produces will also affect how long it takes to charge a drained battery.

If your car has an alternator that produces high amperage (120 amps), then you’ll need less time than if it produces lower amperage (80 amps).

Can A Completely Dead Battery Be Recharged?

A completely dead battery is one that has been drained of all its energy and is inoperable. It can be recharged, but the process can take a long time and may not be successful.

The alternator is designed to recharge your car’s battery when you are driving, so if your battery is completely dead, you will need to drive in order for it to be recharged.

4 Signs of a dead battery

Look for these four signs of a dead battery:

1. Your car won’t start.

It’s a fact: You can’t run your car if there’s no juice in the battery. And while it might not always be easy to tell when your car is struggling to start, there are some signs that you need to look out for.

Your car won’t start. If your car doesn’t want to start up, and you’ve tried everything (turning it on, turning it off, pumping the gas pedal), then it’s time to check the battery.

The lights dim or go out completely when you turn on the ignition. If this happens, it means that your battery isn’t getting enough power from the alternator.

2. Engine is cranking slowly.

Your car battery is a big part of your vehicle’s engine, so if it goes out, your engine won’t be able to start properly.

If you notice that your car is cranking slowly, or not at all, that’s an indicator that your battery may be dead. If you hear clicking noises when you turn the ignition key, or if you notice an odor coming from the interior of your car, those are other signs that your battery could be on its way out.

3. The battery terminals are corroded.

This is a pretty common sign of a dead battery. When the battery is constantly drawing power, it can cause corrosion on the battery terminals. This is also a sign that you may need to get your battery replaced soon, because this corrosion can lead to electrical issues in your car.

4. Your car’s warning lights are on.

If your car’s battery is going bad, you’ll probably notice a few warning signs before it actually dies. One of the most common is that your car’s warning lights will start to flash. This could mean that your alternator is about to fail, or that your battery needs replacing.


In conclusion, an alternator is able to charge a dead battery, but only if the battery has been disconnected and the alternator is in good condition.

If you have a car that has an alternator that isn’t working properly, you may want to consider replacing it with one that does work.

And if your car does not have an alternator at all, then you’ll need to get a new one installed before you can use it.

Now that you also know the signs of a dead battery in a car, you can better prepare yourself if your battery ever fails. You should also be able to diagnose the problem with the help of this guide.

Steven Hatman
Steven Hatman

We break down every information into easy-to-understand articles that cover all the categories anyone who owns a car needs to know about, such as oil , brakes , tires and etc. Our car guide is free and updated regularly for you to use as a resource, not only when you have an issue with your car but even before buying a new or used car! We also give tips on what to look for in each category or part of your vehicle.