Take charge of your battery maintenance

Batteries! You either love them or hate them. There is no in between. You love them for the convenience of being able to carry around electronic devices without being tethered to an electrical cord. Or you hate them because they seem to fail at the most inopportune times. Batteries have become a way of life in a world where the power grid, although reliable, is not 100% fail safe.

By Mike Lewis, Senior Applications Engineer, Megger, Dallas, TX October 1, 2005

Batteries! You either love them or hate them. There is no in between. You love them for the convenience of being able to carry around electronic devices without being tethered to an electrical cord. Or you hate them because they seem to fail at the most inopportune times.

Batteries have become a way of life in a world where the power grid, although reliable, is not 100% fail safe. In today’s information age of data processing, telecommunications and the Internet, backup battery systems have become a necessity to protect data systems and the revenue streams they generate. They also provide emergency power during electrical outages for hospitals and emergency services, and to maintain telecommunications systems during outages. Even the electric utilities use backup battery systems to provide essential electrical services at generating plants. So, what does it take to ensure that these backup batteries are available for duty when called upon? First, let’s look at what makes a battery tick.

Battery basics

All batteries — whether rechargeable or disposable — use chemical reactions to make electricity. Batteries necessarily require two dissimilar metallic materials in a current carrying medium (Fig. 1). In lead-acid batteries, the two dissimilar metallic materials are lead and lead oxide in a sulfuric acid medium. Nickel cadmium (NiCd) batteries use nickel and cadmium compounds in a potassium hydroxide electrolyte medium. Nickel metal hydride (NiMH) is comprised of the same nickel compound as in NiCd cells, but the cadmium compound is replaced with a metallic hydride and the liquid electrolyte is replaced with a paste to carry the current. This article concentrates on the lead acid battery because it is the most common backup battery system in use today (Fig. 2).

Battery hazards

Storage batteries are an extremely useful and, consequently, widely used source of reliable electrical energy. With the proper care and maintenance, storage batteries can also be a very safe method of storing electrical power. However, storage battery systems have been involved in some extremely serious accidents in the past, which will continue unless there is a clear understanding and appreciation of the hazards posed by storage batteries.

Because storage batteries use an electrochemical reaction to produce energy, they present a combination of potential safety hazards. Batteries are not only an electrical hazard but are also chemical and explosive hazards. The acidic or caustic electrolyte presents a potential chemical hazard. The production of oxygen and hydrogen gasses during the electrochemical process presents a potential explosion hazard.

Certain mixtures of oxygen and hydrogen are extremely explosive and can be ignited by an arc or spark. Therefore, NFPA standard 70E requires that ventilation equipment be provided to ensure that the concentration of liberated hydrogen does not exceed 1%. NFPA 70E further requires that access to battery rooms be restricted to authorized (qualified) personnel. Working space around batteries should comply with the standards established for ac equipment.

Battery safety equipment and procedures

Battery systems also present a significant potential for electrical shock hazards. Therefore, standard electrical safety precautions must be observed whenever inspection or maintenance procedures are being performed on these types of systems. In the event of an electrical shock, use standard company procedures to aid in the comfort and care for the injured personnel until qualified medical services arrive.

Working around battery systems also presents a significant chemical hazard due to the presence of either a strong acid (typically sulfuric acid) or caustic (typically potassium hydroxide) electrolyte. Personal protective equipment that should be used to protect against acid/caustic burns includes:

  • Face shield and/or safety goggles to protect the face and neck area from acid/caustic exposure

  • Acid/caustic-resistant apron to protect the body and clothes

  • Acid/caustic-resistant gloves for hand protection

  • Standard chemical safety shoes (general safety precaution) or overshoes.

    • In addition to this personal protective equipment, always ensure that an eyewash and/or emergency drench shower are available for immediate flushing capabilities (Fig. 3).

      ANSI standards require that eyewash facilities be located so that they may be reached within 10 seconds. Industry practice dictates that individuals must not be required to change floors, elevation or working level to reach eye/body wash stations.

      OSHA states in 29 CFR 1910.151(c):

      Where the eyes or body of any person may be exposed to injurious corrosive materials, suitable facilities for quick drenching or flushing of the eyes and body shall be provided within the work area for immediate emergency use. Special hand tools should be used for battery maintenance to reduce the possibility of arcs or sparks that can trigger an explosion of built up explosive gasses. These tools are made of nonsparking materials to eliminate them as possible ignition sources. Tools can also be insulated wherever possible to provide protection against electric shock and ignition-causing arcs and to prevent acid/caustic damage to the tool.

      Additional safety precautions to consider include:

    • Prior to entering the battery room, ensure that the ventilation system is operable and in service

    • Ensure there is sufficient acid/caustic spill neutralizer present. A typical acid neutralizer is bicarbonate of soda (baking soda); common caustic neutralizers are vinegar and boric acid

    • To prevent an explosion, prohibit smoking, open flames and any possible arc-producing activities in the immediate vicinity of the battery room.

      • Battery maintenance

        A battery maintenance schedule encompasses anything from doing nothing (not a good idea) to everything (also not a good idea).

        The following recommended tests are interactive. By examining each test individually, you can gain an understanding of how they interact.

        Float voltage — Float voltage can be one of those misleading tests. While voltage readings of individual cells are important, the sum of the voltages of all the batteries must equal the output of the charger, resistive losses excluded. This condition ensures that the charger is functioning properly. While a normal reading on a cell does not necessarily indicate the condition of that cell, an abnormal reading requires further investigation.

        Specific gravity readings — Sulfate is part of the electrochemical process. If the battery is in a discharged state, some of the sulfate migrates to the plates and the acid is reduced in specific gravity. In a fully charged state, the sulphate is in the acid and the specific gravity is normal, reading approximately 1.215. The tricky part of taking specific gravity readings comes in adjusting the readings for cell and ambient temperatures, because temperature affects the readings considerably. There are no significant studies to validate any correlation between specific gravity and battery capacity. IEEE Standard 450 has deemphasized specific gravity to the point of checking only 10% of the batteries each quarter and the full bank annually.

        Float current readings — Float current results from the difference in potential from the batteries’ self-discharge rates (batteries are always in a self-discharge state) and the chargers’ attempt to keep the batteries fully charged.

        Valve regulated lead acid (VRLA) batteries are prone to a condition called thermal runaway. Because the liquid in a flooded lead acid battery acts as a coolant to help keep the battery from overheating, VRLA batteries are not in liquid form. If the float current increases due to some impending failure or overcharging condition, the temperature increases. The increased temperature allows more current to flow and further increases the temperature of the battery.

        This runaway chemical reaction can lead to melting of the battery, thereby causing an open circuit. The time frame between increases in float current and when thermal runaway can occur is from one to four months. Therefore, float current is an important parameter to measure in VRLA-type battery systems.

        Ripple current readings — Ripple current is a byproduct of the conversion process of converting ac into dc by the rectifier circuit of the charger. Filters in the charger reduce the effects of ripple current. Over time, these circuit components degrade, and ripple current increases. If a component fails completely, the ripple current could increase dramatically. As with float current, an increase in ripple current to a point greater than about 5A RMS for every 100 ampere-hour (Ah) of battery capacity (5%) leads to increased temperature and shortened battery life. Thus, monitoring ripple current periodically ensures proper charger/rectifier operation and helps ensure a healthy battery system. If ripple current exceeds this amount, repair or replace the charger. The first place to look is aging electrolytic filter capacitors.

        Temperature — The effects of temperature extremes in both cell (internal) and ambient (external) conditions have a tremendous impact on battery life. Most backup batteries are designed to last around 20 years at temperatures around 77 F. For every 18 degrees F increase in temperature, the battery life is cut in half. The increased temperature causes faster positive grid corrosion as well as other failure modes.

        Discharge current and time — Online monitoring systems use discharge current and time calculations to determine ampere-hours removed and replaced. The benefit of measuring current and time and calculating ampere-hours removed and replaced is that battery capacity can presumably be calculated. Currently, the only sure way to determine true capacity is the load test.

        Intercell connection resistance — This resistance is one of the more important parameters to test in a battery system, because more than 50% of battery bank failures are related to loose or corroded intercell connectors (Fig. 4).

        The failures can be attributed to frequent outages and/or cycles of discharges and recharges, which cause the lead posts to expand and contract due to the malleability of the lead. The test is simple and can be accomplished in conjunction with other tests, such as impedance testing, or as a stand-alone test with a low-resistance ohmmeter that can measure in the

        Capacity (load test) — The capacity test is the only true method of determining the battery systems’ actual capacity. The drawback is that the test, depending on which method is used (see IEEE Standard 450-2002, page 10 section 7.3), can be time consuming, labor intensive and expensive to perform. The test has limited predictive value depending on how frequently it is performed, because each load test subtracts from the life expectancy of the overall system. Most manufacturers are now recommending capacity tests every 3 to 5 years.

        Impedance — Internal impedance tests measure the capability of a cell to deliver current. The components of impedance — resistive and capacitive reactance — correlate to capacity. Although correlation to capacity is not 100%, it is an excellent way to find weak batteries in the system (Fig. 5).

        An impedance tester applies an ac current signal and measures simultaneously the ac current and the ac voltage drop across a battery caused by the ac signal. Calculate the impedance by dividing the voltage across each battery by the current flowing through it. Impedance is inversely proportional to capacity — as capacity decreases, impedance increases. The test is fast (about 30 minutes for a 60-cell substation battery system) and the system does not have to be taken off line during the test.

        Other tests could be conducted depending on local procedures or the battery manufacturers’ suggested practices. However this list represents the most common tests conducted in the real world and provides the most significant analysis data to determine the health of your battery system.

        Data analysis

        Using the procedures in this article provides you with data about individual components in your battery backup system. In order to make sense of this information, you must decide how best to manage and analyze the information according to your needs.

        The recommended method is to use a database to track and trend all battery test results over time and dispense with forms that don’t compare today’s data with previous data. Specialized databases that provide space to record all measured parameters, can aid in determining the condition of your backup battery system.

        To set limits for certain parameters such as float voltages, follow manufacturers’ guidelines. Other limits, such as internal impedance tests, are more debatable. In some cases, it is advisable to set a “failure limit” of 50% impedance increase for VRLA batteries from a predetermined baseline value. Limits are just that, a set of values you are comfortable with in order to gain the most life from a battery without increasing the risk.


        Whether you love or hate batteries, they must be maintained if you wish them to perform to their full potential. A sound maintenance program will help ensure your system will respond during an emergency and be there to protect critical electrical energy needs when called upon due to outage conditions.

        Proper testing and data analysis can help determine when a battery should be replaced. Scheduled testing routines also help reduce emergency battery replacements and assist in budgetary planning, thus reducing costs.

        The Bottom Line…

      • All batteries use a chemical reaction to make electricity.

      • Follow safe procedures when servicing batteries to reduce injuries and maintain productivity.

      • Regular conducting several common tests will help determine the health of your battery system.

      • Mike Lewis is a Senior Applications Engineer at Megger, focusing on battery and ground testing. If you have questions about battery maintenance you may contact Mr. Lewis directly at (214) 330-3518 or Mike.Lewis@megger.com .

      • Article edited by Jack Smith, Senior Editor, PLANT ENGINEERING magazine, (630) 288-8783, jsmith@reedbusiness.com .

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          When the 2006 Material Handling & Logistics Show and Conference, known as NA 2006 , opens its doors on March 27 at Cleveland’s I-X Center, it will include an educational conference featuring a free executive forum that will provide expertise from industry leaders on breakthrough achievements in high performance supply chains. In addition, more than 60 free show floor educational seminars, an RFID Education Center, two detailed educational workshops and a short course outlining leading-edge equipment and technology solutions will be offered during the NA 2006 Educational Conference .

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