Load Testing Vehicle Batteries in Three Steps

Technicians, Training

Whether you’re driving a big rig with multiple batteries in a bank or driving a compact car with just one battery, it’s important that your batteries be properly maintained. Batteries are the power house of your vehicle, and if they aren’t functioning properly, you’re sure to run into problems. In heavy-duty trucking, that problem often ultimately turns into a road call unless properly taken care of in the shop.

Luckily, properly maintaining and testing a battery isn’t so much difficult as it is easily brushed aside by those who aren’t aware of its importance. In their recent webinar, Larry Rambeaux and Jimmy Fielding discussed battery testing in detail. You can watch the recorded version of the webinar at any time for their full training. However, a summary is provided here:

There are three main steps to load testing a battery.

  1. Physical Examination

Some batteries have a built-in hydrometer that can be used to check the electrolyte in the battery. If your battery does have a hydrometer, there is an eye on top of the battery with a little tube and a green ball that sits down into one of the battery cells. The specific gravity of the electrolyte determines where the green ball sits.

If the battery is fully charged and the specific gravity is high, the green ball will be in the center of the tube, so you can see a green dot in the middle of the eye. If the specific gravity is low, the ball will be shifted to the side so that you see black. If you have somehow lost the electrolyte from the battery, you will see white. At that point you will need to determine why the electrolyte is low.

Check the exterior of the battery case for cracks, broken pieces, leaks, or other damage to the case. The picture below  gives an example of a damaged battery that you would not want to charge or load test. If your battery has damage like this, you’ll want to figure out why the battery is damaged so that the replacement battery is not also damaged. For example, check your battery tie-downs to make sure they are there and that they properly secure the battery.

Once you’ve made sure the case is intact, examine the lead posts. Make sure the threads are not stripped or scuffed up. Also, check the lead pad to make sure it is not damaged—it is your electrical connection. All of the current will flow through that pad, so if it is damaged your system will not work as efficiently, or at all (depending on the severity of the damage to the pad). In addition to checking for damage, make sure the battery and cables are clean. Dirt or grime can also impede the electrical connection.

  1. Determine State of Charge

Determine the battery state of charge of each battery. If the voltage reads higher than 12.75 volts for a flooded cell battery or about 13 volts for an AGM battery, there may be a surface charge on the battery that will interfere with getting accurate results from the load test.

If your load tester is electronic, it will automatically remove the surface charge before conducting the load test. However, if your test equipment is manual, you will need to remove the surface charge yourself by applying a 300-amp load for 15 seconds. After doing this, let the battery sit for a few minutes before conducting the load test.

  1. Load Test

Electronic Equipment:

If you are using an electronic load tester, the tester will ask you to enter the CCA of the battery, battery type, and battery temperature. Make sure you read the exact CCA from the battery rather than assuming you know what it is, because many battery manufacturers make batteries with different CCA ratings that look the same on the outside. The tester asks for the estimated temperature of the battery because the colder a battery is, the less efficient it is. Giving the tester accurate information will allow it to make accurate calculations. The tester will then load test the battery and come back with a result of either good or bad battery.

Manual equipment:

If you are using manual equipment, you’re still going to need the CCA of the battery, battery type, and battery temperature. The difference is you’re going to have to do the math yourself.

Take the rated CCA of the battery and divide it in half, then apply that load for 15 seconds. (For example, if your battery’s CCA is 700, you’ll apply a 350-amp load on the battery for 15 seconds.) At the 15 second mark, you need to read what the voltage of the battery is before you let the load off. If you take off the load before reading the voltage, you’ll end up with a bounce-back voltage, which will not give you an accurate result of your test.

Take that 15-second mark voltage and compare it to the chart below . This is where you need to know the temperature of the battery. If you read 9.2 volts and the battery is at 40° F, the battery fails the load test. At 40° F, the voltage would need to be at least 9.3 volts to pass the load test. However, if the battery is at 30° F, the battery is good because you are above the minimum required voltage.

For more information about load testers or other Purkeys products, contact our team today!