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How to recharge a car battery

As a battery ages, its charge weakens, causing slow engine cranking. A battery may need an occasional “jump” to start it, especially when the car is used for short runs or in cold weather. You can simply replace a weak battery, but with an inexpensive recharger, you can nurse it along for weeks, months, or even longer.

If the dashboard warning light comes on (or the ammeter shows discharge during engine operation), there is a charging-system fault. Have it repaired immediately; recharging will not do the job.

If the battery is refillable, remove the caps and lay a damp rag over the openings while recharging. If it is sealed and has a charge- indicator window in the top, use the charger only if the indicator is green or dark. If it is clear or yellowish, replace the battery.

To recharge a battery, use a tickle charger, a relatively inexpensive device designed to charge a battery at a slow rate. The trickle charger has an electric outlet cord and two wires with alligator clips, one with a red jacket and one with a black or green jacket. Make sure that the car’s ignition is turned off, then connect the red clip to the battery’s positive terminal (marked POS or +) and the other to the negative terminal (marked NEG or -). Be careful not to let the metal clips touch each other or any other metal or they may spark and cause an explosion of the hydrogen gas emitted by the battery. After the charger is connected to the battery, plug the charger into an electric outlet and turn it on. Run the charger for a few hours or overnight. Leave the charger connected until its meter reads less than 1 ampere, then unplug the charger and disconnect the battery.

After recharging, if the battery has removable caps, check it with a hydrometer, an inexpensive device with a float indicating electrical energy in the fluid. If the battery is sealed, test it by trying to start the engine.

If, after recharging, the battery still fails to start the engine, try to jump start the engine. If the engine can be jump started and the charging-system light or ammeter indicates normal operation, the battery is bad; replace it.