Battery maintenance made simple Regular battery maintenance prolongs battery life, keeps the battery fleet in good working condition and provides the user with confidence. Also, fewer batteries are discarded–a direct cost savings.
The need to discharge nickel-cadmium (NiCd) batteries regularly to maintain good performance has concerned users and manufacturers alike. In a desperate attempt to find a maintenance-free battery, some manufacturers went so far as to equip laptop computers and video cameras with the sealed lead-acid (SLA) maintenance-free battery, which proved unsuitable because of its low energy density. Relief was in sight in the early nineties when the nickel metal hydride (NiMH) battery emerged and was promoted as the recommended choice. Claimed to be maintenance-free, the NiMH is commonly used for cellphones and notebook computers.
With twice the energy density compared to the NiCd, the new lithium-ion (Li-ion) battery is expected to be a popular choice when it becomes readily available. Cost has limited this chemistry to high-end applications, such as notebook computers and specialty video cameras.
Frustrated with high operational cost, poor load characteristics and limited cycle life of the newer battery chemistries, manufacturers are now re-examining the old familiar NiCd, and with good reasons. When properly maintained, the NiCd delivers an impressive 1,500 discharge-charge cycles, a service life three times higher than that of the NiMH or Li-ion. At a cost of only a few pennies per cycle, the NiCd is far more economical to operate than the NiMH or Li-ion. If a NiCd battery fails to provide superior cycle count compared to the other chemistries, lack of exercise is likely the cause.
Battery maintenance The notion of having to apply regular discharge cycles becomes an acceptable alternative when considering the low operational cost of the NiCd. Because most applications do not use up all energy before recharge, a discharge to 1V per cell (exercise) is essential for the NiCd to prevent the buildup of crystalline formation on the cell plates. Also known as “memory,” this phenomenon eventually robs the battery of its ability to hold charge. The capacity loss caused by memory is, to a certain extent, reversible.
If used daily, the NiCd should be exercised once per month. The NiMH is also affected by memory but to a lesser amount–it only needs exercise once every three months. Because of its shorter cycle life, it is not recommended to over-exercise the NiMH.
If no exercise is applied for several months, the crystalline formations ingrain themselves, making it more difficult to dissolve. In such a case, exercise is no longer effective in restoring a battery and recondition is required. Recondition is a slow, deep discharge that drains the battery of its remaining energy during which the crystalline structure is broken down and the battery is commonly restored.
The importance of exercise and recondition on NiCd batteries is emphasized by a recent study carried out by GTE Government Systems in Virginia, USA. To determine what percentage of batteries needed replacing within the first year of use, one group of batteries received charge only, another group was exercised and a third group received recondition. The batteries studied were used for portable radios on the aircraft carriers USS Eisenhower, USS George Washington and destroyer USS Ponce.
Table 1 on page 16 shows a 45% battery failure when charge only was used. By applying exercise, the failure was reduced to 15%. By far the best results were achieved with recondition; the failure rate dropped to a low 5%. The same results were obtained on all three ships.
The GTE report states further that a $2,500 battery analyzer featuring exercise-and-recondition functions would pay for itself in less than one month on battery savings alone. No mention was made on the benefits of increased system reliability, an issue that is of equal or greater importance.
Exercise and recondition are most effective when applied while the batteries are still in reasonably good condition. Once the crystalline formation has advanced beyond a certain stage, restoration becomes difficult, even with recondition. If restored, a battery with advanced memory may exhibit a high self-discharge, a deficiency that can no longer be corrected. High self-discharge occurs when the spike-like crystalline formation punctures the fragile separator material that insulates the negative and positive plates. By regularly exercising the batteries, the crystalline formation is kept under control, preventing undue damage to the separator.
Battery maintenance system Any organization using NiCd batteries on a daily routine should set up a battery maintenance system to exercise good batteries, rejuvenate those that fall below a set target capacity and “weed out” the deadwood. Most companies service their batteries either when they no longer hold charge or when the equipment is sent in for repair. As a result, the system becomes unreliable over time, and battery-related failures become frequent. On a routine day, a marginal battery may hold out fine; during an emergency, however, when more energy is required, a poorly performing battery cannot provide the extra power that is needed, and the system subsequently fails.
Implementing a battery maintenance plan requires some effort on behalf of management in sorting the batteries to be serviced and collecting them in one place without disrupting the operation. Certain organizations service the batteries in-house with their own battery analyzers, and others prefer to send them to an independent firm specializing in that service. In both instances, a set of spare batteries will be required to replace those that have been removed.
If the service is done on location and the batteries can be reinstated within 24 hours, only 10 spares in a fleet of 100 batteries are required. If the batteries are sent away, 10 spares are needed for each day they are away. If absent for one week, for example, 70 spares will be needed for a fleet of 100.
After service, the batteries are marked to identify the date of service. One simple method is to attach a color dot, each color indicating the month of service. A different color dot is applied when the battery is reserviced the following month. A numbering system from 1 to 12 identifying the month of service also works well.
Many users prefer to attach a full battery label containing service date and capacity. (See Figure 1 on page 22.) With the label method, a user requiring a battery for a critical mission can examine the state of the battery by simply reading the label. A battery with the highest capacity and the most recent date will undoubtedly be chosen. Battery analyzers are now available that automatically print a label with date, company inscription and battery capacity when the battery is removed.
A key to successful battery maintenance is a good battery analyzer. When first acquiring an analyzer, there is a tendency to buy on price alone. With the requirement of servicing an ever-increasing number of different battery types at higher volumes, second-generation buyers find the features offered on the newer battery analyzers worth the extra cost. The benefits manifest themselves in higher battery recovery, reduced operator time, increased throughput, simpler operation and the use of fewer trained staff members.
One analyzer, for example, evaluates the condition of a battery and applies a recondition cycle to restore the battery’s capacity if a preset performance level cannot be reached. User-programmable switch-mode drivers test the batteries against preset limits, reducing the cycle time by as much as one third compared to fixed-current units. The capacity is displayed in percentage rather than milliampere-hours, freeing the user from memorizing the battery ratings. Each analyzer is capable of processing four batteries every 4-8 hours. Based on two batches per day (morning and evening attendance) and 20 working days per month, one unit is capable of servicing 160 batteries each month. By running an extra shift and increasing the number of working days to 30, the throughput can be doubled.
For larger throughput, Windows-based application software can be used to network as many as 32 analyzers to a host computer. Fully extended, the system is capable of servicing 128 batteries simultaneously.
The software collects battery test results for the database from which inventory status, service reports and graphs are generated. Battery cups and “smart cables” are programmable either through the analyzer’s keypad, the computer keyboard or the optional bar code reader. Custom programs and firmware upgrades for the analyzer can be installed through the host computer. Battery ID numbers and battery characteristics (chemistry, voltage, rating) may be printed on bar code labels and attached to the batteries. By reading the bar code labels, the battery to be serviced is identified, and the battery analyzer is automatically configured to the correct limits for the battery intended.
Conclusion The requirement for regular battery maintenance cannot be emphasized strongly enough, both in terms of prolonging battery life and in keeping the battery fleet in good working condition. Without any means of measuring the performance of aging batteries, a battery fleet eventually deteriorates to a point where it becomes completely unreliable. For NiCd users, the battery maintenance serves two functions: a) to prevent memory from occurring, and b) to maximize the service life of a battery. Organizations using the battery maintenance method have experienced an increase of battery life by one year and more.
There is a time when a battery must be retired, and the battery maintenance system helps to determine when the time is right. With proper battery maintenance, the number of batteries discarded are fewer, a direct cost savings. More important, well-managed batteries provide the user with a level of confidence that is essential when working with today’s hand-held technology.
