How Do I Check My Car Battery?Checking Battery and Charging System: WARNING! Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when you are near the battery or engine. A battery is filled with explosive gasses that can ignite when extreme heat or a spark is present. A battery could have residual acid on the outside casing so use caution when handling a battery and the surrounding area. Use baking soda to neutralize any suspected acid residue before work begins. Wear protective eye wear and clothing and remove all jewelry when checking your battery and charging system. Jewelry is a good conductor of electricity and is not recommended. Most batteries wear out every 3 to 5 years and need to be replaced. Always replace your battery with an equal replacement battery to assure proper operation. Automotive batteries have a +positive terminal (red), - negative terminal (black). The battery in this illustration has a protective cover over the positive terminal to prevent short circuit in case of an accident. Electricity is stored in the battery and then supplied to the vehicle when the engine is not running. While the engine is running the vehicles alternator charges the battery for future use. Step 1 - Checking Battery 
To check a battery surface voltage, remove the positive terminal protective cover. Connect the +positive side meter lead (red) to the positive side battery terminal. Connect the - negative (black) side meter lead to the negative battery terminal. With the vehicle not running and the car sitting over night the battery voltage should be between 12.5 and 12.8 volts. Step 2 - Identify Alternator 
The alternator is rotated by a drive belt driven by the vehicles engine while it is running. Electrical voltage and amperage are generated to recharge the battery and supply voltage to the electrical system of the car. The alternator is held in place with mounting bolts. There is a main electrical wire on the rear of the alternator that supplies voltage to a main voltage junction box. If your alternator is not charging properly, your battery will slowly drain down from operating all the electrical systems in your car and stop the car from running. Step 3 - Checking Alternator Output  +
Connect the voltage meter lead the same way you would in a battery static voltage check, Start engine (do not drive) at engine idle the voltage should be between 13.6 to 14.3 volts. If not the alternator may need replacing. Common Problems: 1. alternator stops producing electrical power and the car stops because the battery dies. 2. battery fails do to age or defect. 3. battery cables become loose causing the electrical system to fail. 
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