How Can I Recharge a Dead Battery?

by Sean Lancaster
Recharge your dead battery to extend its life.

Recharge your dead battery to extend its life.

From time to time, drivers unintentionally leave the lights or radio running on the car and let the battery run dead. Automotive and outdoor recreation vehicle batteries are not cheap and most owners try to avoid replacing them any more often than necessary. One way to avoid early replacement is to recharge the battery and determine if it is dead or just in need of a recharge. Recharging the battery can take between a few and 30 hours. If you don't have a battery charger handy, you can let the car's alternator recharge the battery while the engine is running.

Recharging After a Jump Start

Open the hood of your car and locate the battery. Most manufacturers place the battery in either the right-front or left-front of the engine compartment. Clean any corrosion from the battery posts using a stiff wire brush.

Pull the front of another car up next to the battery. Bring the battery of the other car as close to your battery as possible.

Turn off the engine of the running car. Providing that the other car's battery is fully charged, it will have enough power to start the car with your battery connected to it.

Connect a pair of battery cables between the two cars. The order that you connect the cables is important. Connect the red (positive) jumper cable ends to the two positive posts of the two batteries -- the one on the dead battery first. Connect the black (negative) jumper cable first to the negative post of the car with the functioning battery and then connect the other negative clamp to a piece of unpainted metal on the car with the dead battery -- as far from it as you can. This is to obviate the possibility of an explosion, even though this is not likely.

Start the engine of the other car and rev it up for a few minutes. After revving the car's engine, try to start your car. If you have trouble, check the cables and ensure you have attached the cables firmly to both vehicles.

Remove the jumper cables in the reverse order of the way you attached them. Allow the car to idle for 30 minutes or drive it, to recharge the battery. Then, take the battery to a battery charger to get a full recharge. If the battery fails to hold the charge after using the battery charger and you can't start your car, you need to purchase a new battery.

Charging with a Battery Charger

Take your battery charger near the front of the car with the hood opened. There is no need to remove the battery from the vehicle to use the battery charger to recharge your battery.

Turn the battery charger off and ensure that the plug is not in the wall socket. This minimizes the chance of an accidental shock when hooking up the battery.

Connect the positive lead of the charger to the positive post of the battery and the negative lead of the charger to the engine block or car frame. Most cars have a negative ground and you hook up the charger as outlined, but for cars that have a positive ground -- this is very uncommon -- hook the charger up in the reverse. For a positive-ground car, connect the negative lead of the charger to the negative pole of the battery and the positive lead to the car frame or engine block.

Set the controls of the charger, if present, to 12V, charging current value,;select between manual and automatic and set the time on the timer, if the charger has one.

Plug the charger into the wall socket. Ensure the plug and wall socket are equipped for grounded prongs.

Check the ammeter on the charger to check that the charger is charging the battery. Allow the charger to run until charging stops; depending on the charge level of the battery this may require at least 24 hours. Most chargers have a trickle charger that will keep the battery charged until it is disconnected. The trickle charging occurs at lower amperage than the normal mode.

Unplug the battery charger and move the switch selector to the "Off" position. Remove the charger clip attached to the car frame or engine block. Finally, unclip the lead attached to the battery post.

Use a voltmeter to test the voltage between the two posts on the battery. If the battery shows no charge, you will have to replace the battery.

Items you will need

  • Stiff wire brush
  • Another functioning car
  • Battery cables
  • Battery charger
  • Voltmeter


  • Wear protective safety equipment when working on batteries to guard against fumes and possible explosion or splattering of acid.

About the Author

Sean Lancaster has been a freelance writer since 2007. He has written for Writers Research Group, Alexis Writing and the Lebanon Chamber of Commerce. Lancaster holds a Doctor of Philosophy in chemistry from the University of Washington.

Photo Credits

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