Proper Battery Testing Procedure and Correct Methods

Even many engineers do not know how important it is to test batteries and what is the proper practice to do it. They waste batteries terribly and don’t necessarily care to take notice if something bad is happening. Improper maintenance can make the battery dead, rupture, or in the worst case, violently explode. So it is not always a loss of financials, but it can become hazardous to health and the environment. By adopting sufficient battery testing procedure and proper maintenance, we can improve the overall system’s performance and economic savings over the system’s lifetime.

I am going to present some technical and practical wisdom logically. This article will be worth reading for anyone related to electricity.

Why do batteries fail?

Lead-Acid batteries are supposed to last 4 years, but only 30% of batteries sold today achieve that mark. Lithium-ion batteries are costly, and their loss means a significant loss of money. Batteries are consumable items. Although the failure of batteries is a natural phenomenon, due to aging, inappropriate maintenance and insufficient testing can lead the battery to deteriorate and fail before its useful life.

Useful Tip: If you want to install a battery or uninstall it for a reason like relocating it or checking open circuit voltage, then there is a common rule followed with negative cable, which is first-off last-on. The negative cable is disconnected first and connected last during cable installation and removal, respectively. This helps in minimizing sparks.

Preparation before battery testing

Before testing any battery, the first and foremost thing to do is to take a glance at the appearance of the battery. Look for signs of physical abuse, wear & tear, carrier vibrations, ventilation, electrolyte leak, and heat intensity. Sometimes, careful inspection of the system is enough to find a problematic battery.

Then you need to remove the surface charge, which might be accumulated on plates. To do that, you need to discharge it slightly through load before testing. Discharging with a quarter of the battery’s cold-cranking amps for about 15 seconds will be enough. Wear hand gloves and safety goggles for personal protection. Remember, you are dealing with a container of dangerous fluid and a high density stored charge. Some of the following tests require trained personnel and special equipment. So make sure you take precautions.

How to test batteries with a multimeter?

If you have a multimeter, then you must check the battery’s terminal voltage, battery connectors, and surface drain periodically.

Terminal to Terminal

If the battery is all set visibly, then the first thing for checking the battery’s health is to note Battery’s State-of-Charge. We can connect the voltmeter across the battery’s positive and negative terminals to note the voltage readings. Different battery types have different voltage charts to get existing available capacity. State-of-Charge can show a dead cell in a battery or a bad battery in a battery bank. If you leave a dead cell or battery in a bank running for long, then your other healthy batteries will also die in some time. Because dead cell generates heat, which will affect nearby cells and create stress on other batteries due to drop of amperage rating. The bad battery makes other connected batteries to not fully charged and not last long because other batteries will constantly charge bad ones due to difference in voltage. Also, a good State-of-Charge does not necessarily mean that battery is good too. To check that, you must measure cold-cranking amps. Cold-cranking amps refer to the number of amperes a new lead-acid battery at 0 OF (-18 OC) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery).

Terminal to Electrical Cable

The next step is to check battery connections. Put one test-lead on the positive terminal of battery, and another one on the electrical cable end, which is connected to the positive battery terminal. There should be zero voltage drop. Now do the same thing with the negative battery terminal and cable attached to it. If the voltmeter does not show zero potential difference, then that means the connection is bad. Over time, battery cables become loose. The reduced contact area between terminal and cable will cause an increase in current density. Higher current density in lower contact areas can cause sparks to develop and create heating & burning. This loss of energy can reduce the available voltage supplied to the load. If connections are not rectified, then the battery cause lighting to dim and may fail to start motors and engine. Examination of cables, screws, lugs, clamps, terminals, for breakage & damage, and tightening of loose connections is the way to deal with this problem.

Terminal to Casing

The next test that everyone should conduct is known as the surface drain test. Dust and grime can form a conductive path and cause leakage current to flow over the outer case. The battery’s external body, which comprises a container to store electrolytes, is made up of an insulator. Realistically, no insulator is a perfect insulator, therefore, no insulator shows infinite resistance. Every insulator has some conductance, reciprocal to its resistance. This conductance allows some leakage current to flow continuously from one terminal of the battery to another, even when the system is turned off. The current is usually in the range of nano-amperes for batteries with voltage greater than 12V. Leakage current together with insulator resistance becomes a reason for the development of a potential difference between body and terminal. As a result, it can slowly drain batteries. Salt is a conductor of electricity. In a high humidity environment, salt particles in moisture and dust can increase the conductivity on the surface. Voltage should be checked by touching one probe to a terminal and the second to the outer case. The voltmeter should read value as close to zero as possible for good insulation between the case and terminals.

Impedance Testing

One of the best ways to check the battery’s State-of-Health is to measure Battery’s internal resistance. The test performed for this measurement, by injecting 1 kHz frequency AC into it, is known as the impedance test. As we know, the terminal voltage of batteries depends on the difference between electromotive force and internal resistance voltage drop. A high-value internal resistance, together with the current withdrawn by the load, can lead to a significant loss of energy. Total effective internal resistance indicates the general condition of the battery. It is equivalent to the sum of electrical resistance and ionic resistance. Electrical resistance comprises internal circuitry resistive components, such as conductivity of plates, metal cover, and their surface area of contact. Ionic resistance depends on chemical factors such as electrolyte concentration, ion mobility, type of ions, electrodes geometrical surface area, and polarization. Total effective internal resistance is recorded in the range of milliohms (1 mΩ to 1 Ω). Increasing value over few testing occasions indicates a declination of battery capacity and aging. The degradation trend by tracking performance history is used to identify the irregular and weakest cells in a battery. Impedance tests can also figure out vulnerability in cell and intercell connectors.

Discharge test / Load test

Notable discharge testing methods include load bank testing, capacity testing, partial discharge, and charge/discharge cycle testing.

Load Bank Test

The first one is load bank testing. It is the most comprehensive test by which someone can evaluate battery truly. It verifies that the battery can supply its specified power when it is required. To deliver a surge of power when needed is a sign of a battery with good State-of-Health. It is dominantly conducted for Uninterrupted-Power-Supply and generators with the help of an artificial adjustable load tester. An electrical load bank is used to simulate and mimic the expected conditions of actual resistive and reactive loads faced by the battery. For example, for an automotive system, the load bank follows the driving pattern. For a domestic solar power system, load bank behaves as commercial appliances. It is usually performed at the time of installation and is repeated annually. As I had mentioned above, cold cranking amps is the crucial way for judging the battery’s health apart from the battery’s charge. In a standard test, the battery is loaded with 50% of its cold-cranking amps mentioned by the manufacturer for 15 second duration. For a 12 Volt lead-acid battery, if the voltage does not drop below 10 Volts, over sudden demand of power, then that means the battery is good.

Capacity Test

While we use the above method for calculating the behavior of the battery at peak load, the second one utilizes a constant rate discharge tester for a normal load. This test is the only way of knowing if the battery will perform the same as the manufacturer has prescribed. The battery is forced to deliver pre-set constant current until it is discharged fully. And time is measured to note how long it takes for the terminal voltage to be dropped to discharged level voltage. This way, the capacity of the battery is fully realized. This test is carried out with deep cycle batteries because only deep cycle batteries have the ability to discharge themselves completely with no significant damage to health. But this test takes too much time. For example, a 100 Ah battery discharging at 4 Amps will take 25 hours to pass the test. Capacity test also includes usage of hydrometer and thermometer to calculate specific-gravity (relative-density) of electrolyte to determine Depth-of-Discharge.

Another test related to charging and discharging is used at the time of designing battery and evaluating cycles, number of times a battery can be charged or discharged before deteriorating and completing its life.

Specialized test, which at designing stage, a battery may be subjected to, includes Hybrid Power Pulse Characterization (HPPC) test for dynamic performance characterization of energy and power capability of each electrode. Mechanical test for verifying dimensions and stress handling capability. Environmental test to guarantee safety. Calorimetric test to evaluate thermal management. Electromagnetic Compatibility test to assess immunity from surrounding electromagnetic interference, and disturbance to other nearby electronic devices. And many more.

Useful Fact: Battery cannot charge and discharge at the same time. If you use a battery while in charging mode, then either it will charge or it will discharge. Battery will charge if a battery charger is able to deliver power to the battery, and at the same time, directly supply current to the load. If a battery charger cannot fulfill the required current then load will demand remaining current from the battery, which will cause the battery to discharge. The battery charger’s charging voltage is higher than the battery, therefore, load must be able to accept higher voltage during charging.

Why do we need to check the battery?

• To ensure the load is guarded against power outages.
• To protect critical and sensitive equipment.
• To confirm power backup will be available when needed.
• To prevent unexpected failure of the whole system.
• To predict if the battery’s life is ending.
• What can be done to improve its life?
• To find if a battery or part of the battery is needed to be replaced.
• After how long it will need to be replaced?
• To make sure the battery is completely dead flat before replacement.
• To secure revenue streams from the failure of service.

Following are the steps you should take regularly to avoid losses and making batteries last longer.

Battery Maintenance Checklist

• Make sure the battery top case is clean. Free from dirt, dust, and grime.
• In presence of significant surface drain, clean top with baking soda and water.
• Inspecting terminals, lugs, cables, clamps, and screws for any physical damage.
• Making sure all connections are tight.
• Ensuring battery lead is clean and free from corrosion.
• Applying a thin layer of grease around terminals can prevent them from oxidation.
• Check if the battery has sufficient electrolyte. If not, then fill it with distilled water.
• Look for electrolyte on top of the battery, which indicates overfilling or overcharging.
• Look for signs of change of shape of the case. The dent or rupture shows that battery is overheated or overcharged.

Note: I have written this article to share some insights on engineers’ routine tests. There is so much to go deep in. If you have any questions or just want to appreciate my work, then connect with me on LinkedIn/muhammad-noman-khalid. Batteries are used in factories, power plants, UPS, laptops, smartphones, renewable energy system, cars, boats & marine, aircrafts, electric vehicles and many more places. In each place of usage, battery serves different purpose, such as backup in case of interruption or as a primary source of energy for DC loads, as a system of support or as a main energy storage system, as a rechargeable battery or as a non-rechargeable battery. No industrial sector can live without batteries. It is crucial that we monitor battery’s health, manage it, and sustain its life.