How to Recharge a Dead Car Battery With a Bad Alternator

by Justin Melick
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battery charger image by Albert Lozano from

In a correctly functioning vehicle, the battery provides temporary power to start the engine and run accessories like the lights and radio when the engine is switched off. The alternator, on the other hand, provides electricity to power all of the car's functions while the engine is running and also recharges the battery. If the alternator fails the battery will die, since it is not getting recharged. The only permanent solution to this problem is to get a new alternator but you can recharge the battery in the mean time.

Step 1

Jump start your car. If your battery is dead, you can provide a temporary charge to the battery using jumper cables. Connect the cables to a running vehicle and then to your battery. Leave the cables attached for several minutes and have the driver of the working vehicle press down on the accelerator while their vehicle is in park. This will provide a surge of electricity to your battery. Start your car and disconnect the cables.

Step 2

Connect your battery to a portable car battery charger. Make sure the charger is fully charged then attach the red clip to the positive terminal of your battery and the black clip to the negative terminal. The amount of time it will take for the battery to fully recharge will vary depending on the strength of your charger. A ten amp charger will usually take 45 minutes to recharge. Consult your charger's manual for specific recharge times.

Step 3

Connect your battery to a wall charger. If you do not have a portable charger you can connect it to a charger that plugs into an outlet. You can use an extension chord if it is not raining to charge your battery while it is still in the car or remove the battery. Pull the battery out and take it to where your charger is. Make sure it is sitting on a level surface while it charges. Connect the black clamp to the negative terminal and the red clamp to the positive terminal. The LED light on the charger will turn green when the battery is fully charged.

Step 4

Make your own trickle charger. If you do not have a wall charger you can make a trickle charger using a 12V appliance or cell phone charging chord. Simply cut off the connector on the end then seperate the two wires that make up the cable and pull them apart. Strip the ends of the wires. Use a multimeter to determine which wire has the negative charge. Attach a black alligator clip to it. Attach a red alligator clip to the other wire. Clamp the clips onto the battery and plug it it. A 12V charger will take about 12 hours to recharge a dead battery.

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