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Weak battery symptoms

Weak battery symptoms— how to test your car battery

Dash lights coming on doesn’t mean your battery is fully charged

If you turn the key and your dash lights come on, that does not mean the car battery is good. Why? Because it takes very little power to light up your dash lights. In many cases, it only uses a few amps. But starting your engine requires a minimum of 100 amps.

Rapid clicking when you turn the key is a sign of a weak car battery or corroded battery terminals

If you turn the key and hear rapid clicking, that means the starter motor is getting power, just not enough to fully engage the starter drive and crank the engine. Start diagnosing this by removing the battery terminals and cleaning the terminals and posts with a wire brush. Then reconnect and try starting the engine. If it start, then the corrosion was the problem.

Checking your battery with voltmeter only tells you its state of charge, not state of health.

Use a voltmeter to check your car battery voltage. A fully charged battery should read 12.6 volts and 12.2 volts represents a battery that’s 75% discharged. If your battery reads 12.6, that’s not the end of testing. Battery voltage only tells you the battery’s State of Charge (SOC). It does not tell you the battery’s State of Health (SOH).

Use a battery tester to determine the car battery state of health

To determine SOH, you’ll need a modern digital battery tester that performs a simulated load test along with a conductance/resistance test. These tests determine the condition of the lead plates and bus connections inside the battery. A battery can pass the SOC test but fail the SOH test. You should replace a battery that fails the SOH test because its an indication on impending failure.

best car battery tester

Solar BA9 battery and charging system tester

Use a digital battery tester to test your car battery

To conduct a proper test, the battery tester need to know what type of battery it’s testing. If your tester doesn’t have settings for the different types of batteries, it’s obsolete and can’t give you a state of health.

A car battery tester uses a different testing protocol for each type like, starting-lighting-ignition (SLI-also called a flooded lead acid battery), Absorbed Glass Mat (AGM), Spiral wound glass mat (Spiral), or Lithium (LiFePO4, LFP).

The “toaster” battery shown below is NOT reliable because it doesn’t have settings for SLI, AGM, or Spiral, so it will produce inconsistent results.

dead car battery

“Toaster” style battery tester

inductive ammeter

The Solar BA9 battery testing is an affordable tester that tests all the batteries above except lithium.
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© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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