Mechanics

Battery Test

Step by step testing guide on how to test an automotive battery. This article pertains to all non hybrid and electric vehicles.

Difficulty Scale: 2 of 10

Tools and Supplies Needed

  • Voltmeter
  • Protective eyewear and gloves
Begin with the car on level ground, parking brake on, engine OFF.


Car Battery

Step 1 - If the engine's alternator is not functioning proper it will allow the battery to drain down. Visit - Alternator testing

Step 2 - Use a voltmeter and connect the leads to their respective terminals (black - negative, red - positive.) This will check the batteries surface voltage and its ability to hold a charge. Voltage should read 12.4 to 12.6 volts. (Note: New battery goes dead overnight. Visit - Battery goes dead overnight.)


Checking Surface Voltage

Step 3 - All batteries must withstand a load test which simulates the engine being cranked over by the starter motor. Begin by turning the headlights to the "ON" position. Next, crank the engine over while observing the headlight brightness. The headlights should only dim slightly when using the starter, if they dim way down, or go out, the battery can not supply the amperage needed to operate correctly and must be replaced. As a secondary test, turn the headlights on for 15 minuets, if the battery fails replacement is needed.


Head Lights On - Load Test Battery

Once you have concluded the battery has failed please visit - Battery replacement

Helpful Information

Never connect anything across battery terminals to create a short, this can cause the battery to explode. A car battery is a high amperage-low voltage unit that can deliver a high amount of amperage very quickly and can cause burns and possible fire. Never disconnect a battery when the engine is running, this can cause electrical system and computer damage. Most car batteries must have a "rest" or "down" time to allow the plates inside the battery time to cool. If a battery is subject to constant charge and discharge it will fail prematurely. Also, a battery cannot be discharged completely and then recharged more than a few of times before the battery fails unless its a "deep cycle" type battery. A car battery is hazardous material so you must dispose of your old battery at a local car part store or recycle center.

Common Problems

  • The alternator fails producing no electrical power causing the engine to stall.
  • Battery fails due to age or internal defect.
  • Battery cables become loose, causing the electrical system to fail and the engine to stall.

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-26)