Hard starting, faulty operation of electrical accessories or the battery going dead overnight are symptoms that there may be something wrong with your car's charging system. The battery is just one component of that system. It is, however, the easiest to replace and service. If you are experiencing problems with your car's electrical system, the battery is the first thing to check.
What you will need
1. A DC voltmeter
2. A set of box-end wrenches (metric or SAE, depending on whether your car is foreign or domestic)
3. A wire brush
4. For batteries that are not factory-sealed: hydrometer, distilled water
Charging light on
This is the car's warning system telling you that the battery is not being sufficiently charged. This could be due to an internal fault in the battery, or because the alternator is not putting out a sufficient charge. To test whether sufficient voltage is reaching the battery, place the probes of the voltmeter onto the terminals of the battery while the car is running (positive to positive, negative to negative). The meter should indicate approximately 14 volts. If the meter indicates 13 volts or less, the fault is in the alternator, not the battery. If the meter indicates 14 volts or more, then sufficient voltage is reaching the battery, and the battery is likely faulty and/or needs servicing.
Battery goes dead when car is sitting
This can be due either to there being a slow drain on the battery, such as a dome or trunk light left on or to the battery itself being faulty. A simple test is to disconnect the battery and leave the car sitting overnight. If the battery remains fully charged, there is a drain and/or a short in the electrical system and not the battery.
Hard/slow cranking of the starter
This could be due to either a fault in the starter itself or the battery's failing to deliver sufficient voltage to the starter. Use the voltmeter to test the battery's voltage while the engine is shut off. It should be just over 12 volts. If the battery passes this test, then use jumper cables to connect a second battery (or install another known, good battery) and see if the starter turns properly. If it still does not turn properly, then the problem is with the starter.
Servicing the battery
If your battery is not the kind with sealed cells, it may be possible to add distilled water to the battery's cells and restore its performance. Carefully pry of the caps the cells with a screwdriver and add small amounts of water until the cells are full. If you have a hydrometer, this is the time to check the state of the battery's charge. Insert the hydrometer into one of the open cells and withdraw a portion of electrolyte, then consult the hydrometer reading.
If your battery has sealed cells, then you can't service it. Getting a replacement is the only option.
Replacing the battery
Using the box end wrenches, first remove the negative terminals and then the positive. Be careful not to allow the other end of the wrench to touch anything else, including the other terminal post of the battery. Use the wire brush to clean the terminals. Install the new battery, being careful to position it the same way as the old battery. Make doubly sure that the negative cable is being reattached to the negative post and the positive to the positive. First connect first the negative cable, then the positive. Make sure that the terminals fit snugly all the way down the posts. Tighten securely.
Any time you handle a car battery, wash your hands thoroughly, as battery acid residue can linger on your hands.
Safety precautions
It's always to a good idea to wear eye protection, rubber gloves, a shop apron or old clothes whenever handling a battery.
Tags: sufficient voltage, system battery, battery being, distilled water, electrical system, electrical system battery, indicates volts