How Do I Repair My Car? / How Do I Check a Car Battery?

How Do I Check My Car Battery?

• Car is making a chirping noise
• How to reprogram a key fob remote control
• How does a starter and solenoid work?
• Howling noise from car
• No taillights or taillight light bulb out

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. (Note: never disconnect the battery while the engine is running. If the battery cable is disconnected from the battery a spark can be generated which can cause the battery to explode or a major electrical malfunction to occur.)

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.

Step 4 - Checking Alternator Amperage Output

Testing the amperage output of the alternator is good for measuring the amount (not the level) of voltage the alternator can produce. This test can be tricky because if the alternator is weak it can still show it as producing amperage. Which is good, but if the voltage is low, it will still allow the battery to go dead. To check the amperage output of an alternator an amp meter is needed. Once the meter is connected start the engine. Next turn on all electrical accessories and raise the engine idle to about 1200 RPM. The alternator should output the max amperage it was designed to produce. Example: a 90 amp alternator should output about 88 amps. Note: An alternator cannot sustain maximum output for long periods of time. If the alternator is forced to operate at maximum output it will overheat and fail. An alternator is designed to operate at max amperage output only for a reasonable amount of time.

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.

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.

How Do I Repair My Car? / How Do I Check a Car Battery?

Additional Resources

• Why does my engine stall at idle?
• How do I change my spark plugs?
• Why does my engine crank over but not start?
• Why won't my engine crank over?
• How do I test the engine ignition system?
• Why does my engine over heat?

Additional "How to" Car Repair or Services

• How to Replace Front Brake Pads
• How to Replace Rear Brake Pads
• How to Replace Air Filter
• How to Change a Cabin filter
• How to Change Oil and Filter
• How to Tune Up with Throttle Bore Service
• How to Replace a Radiator
• How to Replace Fuel Filter
• How to Read Trouble Codes

ASK CAR BATTERY QUESTIONS - Join our question and answer forum where free auto repair questions are answered every month, after you have completed our free signup you will able to ask a question and receive an answer from one of our many forum members. If you elect to donate any small amount of money we will assign one of our 2CarPros Certified Repair Technicians to answer your question. Questions with donations are answered promptly and 100% of the donation is awarded to the technician helping you.

GET ONLINE CAR REPAIR MANUALS - Get instant access to your vehicles wiring diagrams, firing orders, component locator, vacuum diagrams, repair procedures, specific testing and diagnostics for troubleshooting, steering and suspension information, heating and air-conditioning problems, safety belt and airbag restraint repair, factory bulletins and general information and much more. We recommend that anyone needing technical repair information should have a quality auto repair manual for their car.