If your car's battery isn't putting out the amps that it should, check it out before you buy a new battery.
Step 1: Protect yourself Put on protective eyewear, gloves, and clothing. Jewelry is a good conductor of electricity, so take it off when you check your battery.
Step 2: Check the battery's age Check the age of the battery. Most wear out after three to five years. Batteries are stamped with a date code, and the manufacture date is usually indicated by the first two characters of the code.
TIP: The first character in the code will indicate the month -- A for January, B for February, through L for December. The second character will indicate the year -- 8 for 2008, 9 for 2009, 0 for 2010.
Step 3: Check the headlights Turn on your headlights. If they are dimmer than usual, the battery voltage and output need to be checked.
Step 4: Use a voltmeter Connect a voltmeter to your battery. If the reading shows less than 12.4, your battery needs to be recharged.
TIP: After you charge the battery, reconnect it to the voltmeter and note the charging voltage. If the voltage registers less than 13.5 volts, you may need to replace your alternator.
Step 5: Check for a power drain Check for a power drain if there is nothing wrong with the charging system or the battery. If there is a high power drain, refer to your owner's manual.
Step 6: Identify the faulty circuit Identify the faulty circuit, and check the relay, switch, module, and other components, replacing as necessary. Pull the fuses and relays one by one until the current reading drops.
Step 7: Check the water level Check the water level of deep cycle batteries, and then charge for at least 16 hours. After this, each cell should be tested with a hydrometer, as load testers give false readings on deep cycle batteries. Now you know if you need to replace your car's battery.
FACT: Nearly 99 million wet-cell lead-acid car batteries are manufactured each year.