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Have you ever jumped in your car, turn the key, and click, click… nothing happens! Your battery is dead! Now, battery failure is the #1 cause of vehicle breakdowns. There are many factors that contribute to how long a battery will last before needing replacement, but typically most batteries will last from 3 to 5 years. More importantly, the battery, charging, and starting systems of any vehicle all need to work together and depend on one another for everything to function correctly. The alternator generates the electricity to operate the vehicle and to re-charge the vehicle’s battery. The battery must be able to store that electricity over time, and be able to supply enough power to the starter motor to spin the engine. The single most important function of all these is to start the vehicles engine. A problem with any one of these systems can lead to poor performance, reduced reliability, and possibly leave you stranded with a car that will not start.
In this article we will show you some simple tests to check your vehicle’s battery, charging system, and starter circuits. Testing these systems is not terribly difficult. You will need a good multimeter that can display DC and AC voltages, and we will also show you to utilize Power Probe testers to accomplish these tests quickly and easily.
Tech Tip #1 – Battery Safety:
Before we get started with our testing, let’s talk about safety precautions when working around batteries. The hydrogen gas that batteries make when charging is very explosive. Batteries can (and do) explode, usually spraying anything around it with sulfuric acid. You must wear proper safety gear to protect yourself in case this happens. Most important, use safety glasses to keep acid from getting in your eyes! If you do not want to get acid on your clothing, wear a protective apron or smock made from acid resistant rubber or polyester. Wearing rubber gloves when handling or working on batteries is also recommended. Remove all jewelry. After all you won’t want to melt your watchband if you are wearing a watch. Just remember you are messing with corrosive acid, explosive gases, and 100’s amps of electrical current.
Tech Tip #2 – Visual Inspection/Charge Battery
The battery and the battery connections are the first items to check. Begin this with a simple visual inspection. Look for obvious problems such as a loose or broken alternator belt, low electrolyte levels, a dirty or wet battery top, corroded or swollen cables, corroded terminals or battery posts, loose hold-down clamps, loose cable terminals, or a leaking or damaged battery case. Repair or replace any items as needed. Distilled water should be used to top off the battery fluid level. Now is also a good time clean any corrosion or residue found around the battery box area or on the battery terminals.
Chances are we began with a car that would not crank, so the battery is likely to be discharged too low to test correctly. Before we can accurately test the battery, it needs to be fully charged. So begin by charging the battery with an appropriate charger to bring the battery back to a 100% SOC (state of charge.) Once the battery is fully charged, we can begin our testing. But first we must remove the residual surface charge on the battery. The surface charge, if not removed, can make a weak battery appear good or a good battery appear bad. Eliminate the surface charge by allowing the battery to sit for between four to twelve hours in a warm room. Another method to remove the surface charge is to discharge the battery for several minutes. Turning headlights (high beam) on for a few minutes will usually do the trick. After turning off the lights you are ready to test the battery.
Tech Tip #3 – Battery Testing
How to measure The Battery State-Of-Charge. You can determine the battery’s State-of-Charge (SoC) by using a Hydrometer to measure the specific gravity of the battery acid, or by measuring the Open Circuit Voltage (OCV) using a digital voltmeter. To determine the battery’s State-of-Charge with the battery’s electrolyte temperature at 80° F (26.7° C), use the following table. The table assumes that a 1.265 specific gravity cell average and 12.65 VDC Open Circuit Voltage reading for a fully charged, wet, lead-acid battery.
If the electrolyte temperature is not 80° F (26.7° C), use the Temperature Compensation table to adjust the Open Circuit Voltage or Specific Gravity readings.
The Specific Gravity or Open Circuit Voltage readings for a battery at 100% State-of-Charge can vary by plate chemistry, so check the manufacturer’s specifications for a fully charged battery.
For non-sealed batteries, check the specific gravity in each cell with a hydrometer and average cells readings. For sealed batteries, measure the Open Circuit Voltage across the battery terminals with a digital voltmeter. This is the only way you can determine the State-of-Charge. Some batteries have a built-in “Magic Eye” hydrometer, which only measures the State-of-Charge in ONE of its six cells. If the built-in indicator is clear, light yellow, or red, then the battery has a low electrolyte level and if non-sealed, should be refilled and recharged before proceeding.
If sealed, the battery is bad and should be replaced. If the State-of-Charge is BELOW 75% using either the specific gravity or voltage test or the built-in hydrometer indicates “bad” (usually dark or white), then the battery needs to be recharged BEFORE proceeding.
Note: You should replace the battery, if one or more of the following conditions occur:
- If there is a .050 or more difference in the specific gravity reading between the highest and lowest cell, this indicates a weak or dead cell(s).
- If the battery will not recharge to a 75% or more State-of-Charge level or if the built-in hydrometer still does not indicate “good” (usually green or blue, which indicates a 65% State-of-Charge or better).
- If a digital voltmeter indicates 0 volts, then there is an open cell in the battery.
- If the digital voltmeter indicates 10.45 to 10.65 volts, there probably is a shorted cell. A shorted cell is caused by plates touching, sediment build-up or “treeing” between the plates.
Using the Power Probe 3, we can easily check the battery’s OCV by simply connecting the PP3 to the battery, and either probing the battery’s positive terminal, or pressing the rocker switch to positive which will display the battery voltage. Using the Power Probe Hook, it is simply a matter of connecting the Hook to the battery and reading the Battery voltage shown on, the Hook’s two line display.