Will A Battery Tender Charge A Dead Battery?

Key Points:

  • It is possible to recharge a dead battery with the help of battery tenders.
  • The battery tender must detect an amount of voltage before it can start the charging process.
  • There are several other methods available for reviving a dead battery.

Batteries lose power inside if they aren’t utilized and recharged on a regular basis. It should take you roughly 10 minutes to connect a battery tender. And thus comes the question, will a battery tender charge a dead battery?

Yes, by using battery tenders, you can charge a dead battery. But before these chargers can work, they must sense a particular level of voltage in most cases. With a battery tender of 0.75 amps, a fully dead battery should take at least 35 to 45 hours, and 20 to 30 hours with a battery tender rated 1.25 amps.

Throughout this article, I will provide you with a comprehensive look into the properties of a battery tender, how to use it, the pros and cons etc. and other questions that you might have regarding this issue. So, without farther ado, let’s begin.

Can a Completely Dead Battery Be Recharged Using a Battery Tender?

When the voltage of a car battery falls below 12 volts, it is called discharged. While the alternator in your vehicle can keep a good battery charged, it was never meant to fully recharge a dead car battery.

But will a battery tender charge a dead battery? Yes, these charging devices called battery tenders are intended to return a dead battery to full charge in a safe manner.

The steps to properly use battery tender to charge a dead battery is provided below:

  • Step 1

If your car is still running, turn it off and take the key from the ignition. Remove the hood.

  • Step 2

Remove the black (negative) battery connector from the battery with an adjustable wrench and set it aside. Remove the automobile battery’s red (positive) battery terminal. Set it off to the side.

  • Step 3

Clamp the battery tender’s red (positive) clamp over the positive battery connection to prevent it from coming off without being manually removed.

Because most cars have a negative ground, which means that part of the line connecting to the battery is tied to the vehicle frame, secure the tender’s black (negative) clip to either the engine block or the vehicle frame.

Do not attach the black clamp to the engine’s hoses, wiring, or moving parts. Positive ground vehicles are uncommon, so check your owner’s handbook or call a local dealer for your car type and ask the service department if you’re not sure.

  • Step 4

Switch the amp switch on the battery tender from “2” to “6” if that particular model has one. Plug in the battery tender to an electrical outlet, using an extension cord if necessary.

  • Step 5

Keep an eye on the battery tender’s light. It’s still charging if it’s red. The battery is completely charged when it turns green.

  • Step 6

Remove the charger from the outlet and unplug it. Remove the black clamp from the engine block or car frame (negative). Remove the battery’s red (positive) clip. Set aside the battery tender.

Use the adjustable wrench to attach the red (positive) battery connector to the positive of the automobile battery.

Place the black (negative) battery terminal to the black negative of the automobile battery and secure it with the wrench.

Make sure all of the connections are solid and tight. Your vehicle’s hood should be closed.

By following these simple steps, you can hook up a battery tender to your dead battery and proceed to charge it. But it might take a long while considering the state of the battery.

What are the Signs of a Dead Battery?

Not all batteries will give you warning indicators that they are about to fail, but some will. While a “dead” battery is commonly characterized as one that cannot start the automobile, there are various other signs that a battery is failing.

A Slower, More Sudden Start

When the temperature drops below 20 degrees, any car’s starting cadence slows. When you reach below 0 degrees, it becomes considerably slower.

If you see similar behavior without the temperature dropping – a sluggish, dragging start – have your battery examined as soon as possible and don’t ignore it. The automobile will eventually stop starting.

If a slow-starting battery appears to be able to charge and test properly, a parasitic drain, or draw, is likely depleting the battery while the car is parked, and the electrical system will need to be examined.

Headlights Light Up, But Doesn’t Start

Your lights and radio both functions, but when you press the key, you hear a click or buzz.

Alternatively, your headlights are really dim. The battery’s job is to start the engine by supplying a large amount of high-amperage electricity to the starter.

When the battery is low, it can’t offer that much power, but it can still power lights and accessories that don’t demand as much power.

Radio Stops Working

Your radio isn’t working. Don’t dismiss it as a small annoyance. The battery powers the radio, windshield wipers, and headlights, among other electronic equipment, when the ignition is turned on. Your battery charge is low if these flicker or fade before beginning.

Battery Swelling

The battery is bloated or obese. Your battery was designed with a precise footprint in mind, and you should be able to see it if it swells in size. The alternator has a broken voltage regulator and has overcharged the battery if you have a bloated battery.

The development of hydrogen gases faster than the battery can dissipate causes the battery to overcharge. The battery has already been damaged, and it cannot be repaired.

Odd Smells Emitting from the Battery

If the battery emits a noxious odor, it’s a clue that it’s about to fail, if it hasn’t already. By definition, a battery has no odor.

If your battery smells like rotten eggs, it has released gas. It also emitted sulfuric acid, which might cause damage to other components of your engine.

So, if you don’t take action to remedy this scent, it might be the most expensive problem on the list.

The “Check Engine” Light Flashes

The check engine light flashes or remains illuminated at all times. This light usually indicates major engine problems that will necessitate costly servicing. However, you could strike it rich and discover that all your automobile needs, is a new battery.

The Car Starts, But Dies Immediately

This is a very strange issue that can indeed happen on certain makes / models of vehicles. The battery will have enough voltage to start the vehicle, but then it immediately dies and will not idle.

If you encounter this issue, there are a multitude of things that could be wrong, but doing a simple battery check is the first and easiest place to start.

The basic behind this is when a battery fails, it can cause interruptions to the constant signals it sends to the ECU. Then if the battery can muster enough might to start the car, the sensors controlling engine idle, speed, and fueling have already lost signal, and the car immediately dies.


Throughout this article I have talked in detail about the ins and outs of battery tenders as well as how to use them. I hope it has helped answer the question, “will a battery tender charge a dead battery?”.

However, it is advised to get a proper diagnosis of your battery by an experienced professional if it is malfunctioning before resorting to any solutions or fixes yourself.

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