|
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.
|