16. Practical Battery Tips
Batteries seem to have a mind of their own. Their stubborn and unpredictable behavior has left many battery users in awkward situations. In fact, the British Army could have lost the Falkland War in 1982 because of uncooperative batteries. The army assumed that a battery would always follow rigid military specifications. Not so. When the order was given to launch the portable missiles, nothing happened and the missiles did not fly that day. Such battery-induced letdowns happen on a daily basis. Some are simply a nuisance, others have serious consequences.
In this section we examine what the user can reasonably expect from a battery. We learn how to cope with the many moods of a battery and how to come to terms with its limitations.
16.1 Personal Field Observations
While working with General Electric, I had the opportunity to examine the behavior of many NiCd batteries for two-way radios. I noticed a trend with these batteries that was unique to NiCd. These particularities repeated themselves in various other applications.
A certain organization continually experienced NiCd battery failure after a relatively short service time. Although the batteries performed at 100 percent when new, their capacity dropped to 20 percent and below within one year. We discovered that their two-way radios were under-utilized; yet the batteries received a full recharge after each short field use.
After replacing the batteries, we advised the organization to exercise the new batteries once per month by discharging them to one-volt-per cell with a subsequent recharge. The first exercise took place after the batteries had been in service for four months. At that stage, we were anxious to find out how much the batteries had deteriorated. Here is what we found:
On half of the batteries tested, the capacity loss was between 25 to 30 percent; on the other half, the losses were around 10 to 20 percent. With exercise — and some needed recondition cycles — all batteries were fully restored. Had maintenance been omitted for much longer, the probability of a full recovery would have been jeopardized.
On another occasion, I noticed that two-way radios used by construction workers experienced fewer NiCd battery problems than those used by security guards. The construction workers often did not turn off the radios when they put down their hammers. As a result, the batteries got their exercise and kept performing well until they fell apart from old age. In many cases the batteries were held together with electrician’s tape.
In comparison, the security guards pampered their batteries to death by giving them light duty and plenty of recharge. These batteries still looked new when they had to be discarded after only 12 months of service. Because of the advanced state of memory, recondition was no longer effective to restore these batteries.
On a further application, I studied the performance of a two-way radio that was available with batteries of different capacities. It soon was apparent that the smaller battery lasted much longer, whereas the larger packs needed replacing more often. The small battery had to work harder and received more exercise during a daily routine.
Equipment manufacturers are aware of the weak link — the battery. For a more reliable energy source, higher capacity batteries are recommended. Not only are oversized batteries bulky, heavy and expensive, they hold more residual charge prior to recharge than smaller units. If the residual energy is never fully consumed before a recharge, and no exercise is applied, the nickel-based battery will eventually lose its ability to hold charge due to memory.
On the lithium and lead-base systems, a slightly oversized battery offers an advantage because the pack is less stressed on deep discharges. The battery does not need to be discharged as low for the given application. A high residual charge before recharge is a benefit rather than a disadvantage for these chemistries.