Can a Battery Tender Charge a Dead Battery?

by Phil Borges // in Car

Yes! A battery tender can charge a dead battery. However, the process will take some time. Even if you have a brand new charger, you might wonder why nothing happens after charging it for almost five hours or more. If that’s the case, don’t miss reading this article to know if it’s normal or if you need to do something to make it in the charging mode. You will also learn how to bring a dead battery back to life by utilizing a battery tender and the correct charger.

Will a Battery Tender charge a dead battery?

Yes, a battery tender can charge a dead battery. Using a battery tender is the best way to charge a dead battery. However, the process will take some time, but you can get your dead car started in the end. Dead batteries could charge for about 20–30 hours using an excellent battery tender charger and could take up to 35–45 hours when using old ones. Unfortunately, these chargers cannot charge an already-depleted battery. In this case, you will need to use a jump starter or charger to get the car started.

What is a battery tender?

You may have thought about what does a battery tender do. Battery tenders are electrical devices that help to recharge your vehicle’s dead battery. This handy tool can prevent the corrosion of car parts, making it possible for you to start your engine immediately and maintain your vehicle all year long without causing additional trouble.

Additionally, a battery tender recharges your batteries back safely without causing explosions or harm to your vehicle’s electronics while charging them with an auto battery charger. 

What are the common types of battery tenders for a dead battery?

A good battery tender includes smart chargers that stop charging once the battery is fully charged, which can be very helpful when a person doesn’t have much time. It would help if you considered different factors before buying one, as some tenders cannot charge an already-depleted battery in an emergency.

Here are the three categories of battery tender chargers: 

  • Smart chargers with automatic shutoff when fully charged
  • Trickle chargers that do not have an automatic shutoff
  • Conventional chargers with an automatic shutoff to prevent overcharging.

smart charger with automatic shutoff will cost you more but is well worth your car’s charging system investment. These chargers have intelligence that allows them to sense when a full charge has been reached and then automatically shut off, preventing any damage from coming to the battery or charger itself. They are also equipped to charge a battery on the hook under your hood or in your trunk.

A trickle charger is a device with a low voltage output. Thus, it “trickles” power into the system over a longer period. While this type of tender can work well if you are going to be gone for an extended time, it isn’t recommended for daily use.

conventional charger works much like the one you have at home for your television or computer. It has an automatic shutoff to prevent overcharging. But, it cannot provide enough power to get a car running again if its battery is dead and it needs jumpstart cables from another vehicle.

Experts also recommend reading the troubleshooting guide in your owner’s manual. If your car won’t start with a jump from another vehicle, it is time to consider replacing the battery.

How to use a battery tender correctly?

  1. Disconnect the battery’s negative terminal.
  2. Connect the positive terminal of the battery tender to the positive terminal of the disconnected car battery.
  3. Connect one end of alligator clips to another end of the positive cable in parallel or series.
  4. Connect a jumper cable to the opposite end.
  5. Finally, you can start charging your battery with a battery charger or any other source.

The manufacturer of your chosen battery tender may inform you that you can leave it connected to the battery for as long as you want. However, removing the tender once your battery is charged is always better. Leaving it in place can cause overcharging, resulting in excessive and irreversible damage to your car battery, affecting starting ability and longevity.

Moreover, many have inquired, “how do I know if my battery tender is bad?” If your battery tender is bad, you may notice that your car’s battery is not charging as quickly as it should. In some cases, the charger may not work at all. If you suspect your battery tender is faulty, you can take it to a qualified mechanic or auto parts store for testing.

Final Thoughts

If your car does not start after several attempts, detecting a low or dead car battery is sufficient to indicate that it’s time to use a battery tender. Always ensure that you use a multimeter to monitor the voltage level of your car battery before you decide to use a battery tender. If you do not have a multimeter, touch the probes of an unused jumper cable to both ends of your car battery and wait for a few seconds. If the reading on the multimeter is above 12.70 or more, your battery is charged enough, and you should remove the battery tender.

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About the author, Phil Borges

Phil Borges is a battery aficionado. He's written extensively about batteries, and he loves nothing more than discussing the latest innovations in the industry. He has a deep understanding of how batteries work, and he's always on the lookout for new ways to improve their performance.