<< Previous page INDEX Next page >>
15.2 Priming
Some nickel-based batteries do not perform well when new. This deficiency is often caused by lack of formatting at the time of manufacturing. Batteries that are not sufficiently formatted are destined to fail because the initial capacity is low. The full potential is only reached after the battery has been cycled a few times. In many cases, the user does not have the patience to wait until the expected performance is reached. Instead, the customer exercises the warranty return option.
The most critical time in a battery’s life is the so-called priming stage. An analogy can be drawn with breaking in a new car engine. The performance and fuel efficiency may not be best at first, but with care and attention, the engine will improve over time. If overstressed when new, the engine may never provide the economical and dependable service that is expected.
Some poorly formatted batteries are known to produce less than 10 percent of capacity at the initial priming stage. By cycling, the capacity increases, and the battery will become usable after three to five cycles. Maximum performance on a NiCd, for example, is reached after 50 to 100 full charge/discharge cycles. This priming function occurs while the battery is being used. The gradual capacity increase during the early life of a battery is normally hidden to the user.
Quality cells from major Japanese manufacturers do not need extended priming and can be used almost immediately. After five full cycles, the performance is predictable and fully repeatable.
The manufacturer’s recommended priming procedure should be followed. In many cases, a 24-hour trickle charge is needed. Verifying the performance with a battery analyzer is advisable, especially if the batteries are used for critical applications.
Some nickel-based batteries are known to form a passivation layer if kept in prolonged storage. Little scientific knowledge is available on this subject and the battery manufacturers may deny the existence of such a layer. A full charge/discharge, followed by a complete recharge corrects the problem.
Li-ion cells need less priming than the nickel-based equivalent. Manufacturers of Li-ion cells insist that priming is not a requirement. The priming function on the Li-ion may be used to verify that the battery is fully functional and produces the capacity required.
In an earlier chapter, the question “Why are excessive quantities of batteries being returned under warranty?” was raised. This question has not been fully answered. It appears that all battery chemistries are represented among the packs being returned. It is unclear whether these batteries are inoperable as claimed. Perhaps the liberal warranty return offered by dealers provides an opportunity to acquire a new, and seemingly better, battery without charge. Some misuse of the warranty policy cannot be fully dismissed.
The internal protection circuit of lithium-based batteries may be the cause of some problems. For safety reasons, many of these batteries do not allow a recharge if the battery has been discharged below 2.5V/cell. If discharged close to 2.5V and the battery is not recharged for a while, self-discharge further discharges the pack below the 2.5V level. If, at this time, the battery is put into the charger, nothing may happen. The battery appears to have an open circuit and the user consequently demands a replacement.
Cadex has received a large number of supposedly dead Li-ion polymer batteries from various manufacturers. When measured, these batteries had no voltage at the terminals and appeared to be dead. Charging the packs in their respective chargers was unsuccessful. But after waking up the battery’s control circuit with the ‘Boost’ function of the Cadex 7000 Series battery analyzer, most of these batteries accepted normal charge. After a full charge, the performance was checked. Almost all packs reached capacities of 80 percent and higher and the batteries were returned to service.