The battery is the heart of the entire electrical system. A thorough battery test is absolutely essential to successful and profitable starting-charging system diagnosis, experts said. Auto electric specialists also emphasized that people underestimate the battery's impact on the starting and charging systems. Battery problems are the root cause of more starter and alternator failures than technicians realize, they said.
A battery converts chemical energy into electrical energy. Hydrogen, a highly explosive gas, is a normal by-product of the chemical reaction inside a battery. Therefore, technicians must take common sense precautions when working around batteries. For example, wear eye protection and keep all flames and sparks away from the battery. Always turn off the ignition switch before connecting or disconnecting the battery.
Never charge a frozen battery because doing so may cause a battery explosion. Always allow the battery to thaw completely first. Note that frozen batteries usually suffer irreversible internal damage.
A quick visual inspection yields a wealth of information about general battery condition. For example, a damp or wet battery top suggests an overcharge condition. The excessive gasing overcharging causes often blisters the paint on the underside of the hood near the battery.
Always check for loose battery terminals and cables on both top- and side-terminal designs. Try to wiggle each battery cable terminal. When the connection feels loose, don't just retighten it because a loose connection is usually a corroded or dirty one. Instead, remove the battery cables and clean both the battery and cable terminals with a proper service tool.
Replace the battery if its terminals are loose in the battery case. The battery may be working now, but loose terminals are a failure waiting to happen. Worse yet, terminals that are loose in the case could lead to a cracked internal connection. In turn, a cracked internal connection may create arcing that leads to a battery explosion. A cracked battery case is also cause to replace the battery.
Be sure the battery is mounted securely. Although today's battery designs are more vibration-resistant than ever, vibration is still one of the battery's biggest enemies. That's why replacing rusted, cracked or damaged battery trays and mounts are part of a thorough battery job.
The last visual check is to compare the ratings on the battery label to specifications. Battery ratings are explained in another part of this service section. A battery that's too weak for the application often is the root cause of the customer's complaints, including premature alternator or starter failure.
Cold cranking amps (CCA) is the main indicator of a battery's strength or capacity. When a battery lacks adequate capacity for the application, many veteran technicians say it's ``too small'' for the vehicle. The expression ``too small'' lingers from the days when a battery's electrical capacity was closely related to its physical size. But thanks to modern technology, the dimensions of a 700 CCA battery often are no larger than those of a 350 CCA unit.
Get in the habit of noting the CCA rating of the original equipment (OE) battery every time you open the hood of a vehicle. Doing so will familiarize you with trends in OE battery capacities, making it easier to detect a battery that's too weak for the application.
When battery capacity is below specification, call it to the customer's attention on the work order. The vehicle may be running fine today. But the potential long-term effects of an under-capacity battery, such as premature alternator and starter failure, may occur later and be blamed on innocent service personnel.
Starting and charging systems depend upon a good battery. Therefore, accurate battery testing is a vital first step in starting-charging system diagnosis. What's more, battery tests are so easy to perform that it's foolish to skip them.
The two main battery tests are the state of charge check and the load test. You can check state of charge with a hydrometer or a high-quality digital voltmeter. The hydrometer checks state of charge by measuring the concentration of the battery electrolyte. Today, the hydrometer has limited usefulness because most automotive batteries are sealed-top designs.
A digital voltmeter is preferable because it's more accurate than common analog meters. Before proceeding, note if the vehicle has been running or if the battery has just been charged. If so, remove the battery's surface charge by applying a 150-amp load to the battery with a load tester. Or, turn the headlights on high beam for about a minute, then shut off the lights.
A surface charge is an unusually high charge lingering on the battery plate surfaces that disturbs the accuracy of the state of charge check.
Next, connect the digital voltmeter directly to the battery terminals and check voltage with the engine and all accessories shut off. A reading of 12.6 volts or more is a fully charged battery, 12.4 volts is 75 percent charged. Recharge the battery before load testing it when its state of charge is less than 12.4 volts.
When the state of charge check shows 10.4-10.5 volts, it's usually a telltale sign of a shorted cell and a defective battery. Beware: a shorted battery cell may strain or damage the vehicle's alternator!
The battery's most demanding task is running the starter motor, cranking the engine. The most accurate battery test, a load test, gauges the battery's performance under an electrical strain similar to the starter motor's. One way to do this is to use the starter motor itself, another is using a load tester device.
Using a load tester is the preferred approach because it performs a controlled but isolated test. This means the tester eliminates factors such as starter cable-starter motor problems and excessive internal engine friction.
A load tester contains a huge variable resistor. When you connect the load tester to the battery and turn on its load control, battery current flows through this resistor and battery voltage drops just as if the starter was
The industry-standard test is to adjust the load control until the tester's ammeter reads one-half the battery's CCA rating, then wait 15 seconds. After 15 seconds, the ``loaded'' battery voltage must not drop below 9.6 volts at room temperature. If it drops below 9.6 by the end of the load test, recharge the battery and repeat the load test. Replace the battery if it flunks another load test.
The minimum passing voltage for a load test varies according to temperature. Temperature-voltage charts are shown in load tester operating guides and service manuals. Plus, some testers have test leads with integral temperature sensors. So, the ``loaded'' battery voltage the tester shows is already adjusted for temperature.
State of the art load testers enhance test accuracy and consistency even more by automatically applying the load you select for exactly 15 seconds, releasing the load and displaying the test results. Other machines have a timer light that blinks once every second of the load test. So, you count 15 blinks and release the load control.
Remember the following points when load-testing batteries. First, routinely zero the load tester ammeter according to the manufacturer's instructions.
Second, carefully apply the load for exactly 15 seconds when using a manual load control. Also, always note the loaded battery voltage before releasing the load control.
Third, experience shows that healthy batteries usually maintain a stable 10.0-11.0 volts throughout the load test. On the other hand, a weak battery's voltage tends to plummet when you turn on the load control.
Fourth, never release the load control and remove the load before the 15-second period has elapsed. Sometimes, the loaded voltage of a bad battery won't falter until the very end of the test period.
Fifth, if you suspect the vehicle's battery is under capacity, watch how battery voltage reacts after you release the load control. If the battery flunked the load test but its voltage climbs back to 12.4 or more after you release the load, the battery probably lacks adequate electrical capacity for the application.
Finally, writing the test results on the work order and explaining them to the customer reduces comebacks and complaints. For example, a battery that just passes the load test at 9.6 volts may not necessarily be a problem. But on a vehicle with a history of hard starts or hard usage, a battery that just passes usually is a failure waiting to happen.
Using the starter
Cranking the engine for 15 seconds may be a suitable alternative to using a load tester-provided the entire cranking circuit and the basic engine are in good condition.
However, problems such as a defective starter cable or motor or a ``tight'' engine upset the accuracy of this test approach.
Disable the ignition or remove the fuel pump fuse so the engine won't start. Where necessary, ground the ignition coil wire to prevent arcing. Connect a digital voltmeter to the battery terminals and crank the engine for 15 seconds.
Note the voltage reading at the 15-second mark before releasing the ignition switch. If the voltage drops below 9.6 volts, recharge the battery and retest.