Mechanics

Battery Load Test

Easy to understand step by step guide on how to test an automotive battery without tools or meters, this information pertains to most vehicles.

Difficulty Scale: 1 of 10

Begin with your vehicle on level ground, parking brake "ON", engine "OFF". Always wear protective eyewear, gloves and necessary clothing before work begins, stand clear of the battery while the engine is cranked over.

WARNING - A battery is filled with acid that produce explosive gasses which can ignite when a spark or flame is present. A battery could have residual acid on the outside casing, use caution when handling, use baking soda to neutralize any acid residue before work begins, never connect anything across battery terminals to create a short, this can cause the battery to explode. Never disconnect a battery when the engine is running, this can cause electrical system and computer damage.

Step 1 - Locate and inspect the battery to ensure a proper connection absent of corrosion. Visit - Battery Cable Cleaning


Battery Terminal Corrosion

Step 2 - Turn the headlights to the "ON" position, wait 15 minutes, the battery must withstand this load test which simulates the engine being cranked over by the starter motor.


Headlights "ON"

Step 3 - Next, crank the engine over while observing the headlight brightness, they should only dim slightly when using the starter, if they dim way down, or go out followed by a machine gun style of clicking noise, the battery can not supply the voltage needed to operate correctly and must be replaced.


Headlights Dim

Helpful Information

As a battery ages it loses the ability to store electrical energy resulting in an insufficient flow to the starter. When a starter is subjected to low voltage/amperage (flow) it will cause the starter to engage and disengage rapidly producing the machine gun like sound.

A battery will not perform as it should if the alternator has failed, or the battery has failed internally and replacement is required. Visit - Alternator testing Visit - Battery replacement

When a battery short circuits internally, the case sides can bulge indicating warped plates which short circuit causing the engine to stall due to a drop in system voltage.

Battery acid and electrolysis can cause corrosion inside the battery cables which will inhibit the electrical flow, look for bulges near the top of the cable, these bulges indicate corrosion expansion caused by the chemical reaction between the acid and copper wire and must be replaced.

A regular battery must have a "rest" or "down" time to allow the plates inside time to cool. A battery subjected to constant charge and complete discharge will fail prematurely unless its a "deep cycle" type. A battery is hazardous material and must be disposed of at a local parts store or recycle center.

Common Problems

  • 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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