To perform a cell voltage test (fig. 2-9), use a low voltage reading voltmeter with special cadmium (acid resistant metal) tips. Insert the tips into each cell, starting at one end of the battery and work your way to the other. Test each cell carefully. If the cells are low, but equal, recharging usually will restore the battery. If cell voltage readings vary more than .2 volts, the battery is BAD.

Figure 2-8.- Battery voltage test performed with a battery tester.

Figure 2-9.- Cell voltage test.

BATTERY DRAIN TEST.- A battery drain test checks for abnormal current draw with the ignition off. If a battery goes dead without being used, you need to check for a current drain.

To perform a battery drain test, set up an ammeter, as shown in figure 2-10. Pull the fuse if the vehicle has a dash clock. Close all doors and trunk (if applicable). Then read the ammeter. If everything is off, there should be a zero reading. Any reading indicates a problem. To help pinpoint the problem, pull fuses one at a time until there is a zero reading on the ammeter. This action isolates the circuit that has the problem.

BATTERY CAPACITY TEST.- A battery load test, also termed a battery capacity test, is the best method to check battery condition. The battery load test measures the current output and performance of the battery under full current load. It is one of the most common and informative battery tests used today.

Before load testing a battery, you must calculate how much current draw should be applied to the battery. If the ampere-hour rating of the battery is given, load the battery to three times its amp-hour rating. For example, if the battery is rated at 60 amp-hours, test the battery at 180 amps (60 x 3 = 180). The majority of the batteries are now rated in SAE cold-cranking amps, instead of amp-hours. To determine the load test for these batteries, divide the cold-crank rating by two. For example, a battery with 400 cold-cranking amps rating should be loaded to 200 amps (400 2 = 200). Connect the battery load tester, as shown in figure 2-11. Turn the control knob until the ammeter reads the correct load for your battery.

Figure 2-10.- Battery drain test setup.

After checking the battery charge and finding the amp load value, you are ready to test battery output. Make sure that the tester is connected properly. Turn the load control knob until the ammeter reads the correct load for your battery. Hold the load for 15 seconds. Next, read the voltmeter while the load is

Figure 2-11.- Instrument hookup for battery capacity test.

applied. Then turn the load control completely off so the battery will not be discharged. If the voltmeter reads 9.5 volts or more at room temperature, the battery is good. If the battery reads below 9.5 volts at room temperature, battery performance is poor. This condition indicates that the battery is not producing enough current to run the starting motor properly.

Familiarize yourself with proper operating procedures for the type of tester you have available. Improper operation of electrical test equipment may result in serious damage to the test equipment or the unit being tested.

QUICK CHARGE TEST.- The quick charge test, also known as 3-minute charge test, determines if the battery is sulfated. If the results of the battery load test are poor, fast charge the battery. Charge the battery for 3 minutes at 30 to 40 amps. Test the voltage while charging. If the voltage goes ABOVE 15.5 volts, the battery plates are sulfated and the battery needs to be replaced.