Chapter 4: Proper Charge Methods
To a large extent, the performance and longevity of rechargeable
batteries depends on the quality of the chargers. Battery
chargers are commonly given low priority, especially on consumer
products. Choosing a quality charger makes sense. This is
especially true when considering the high cost of battery
replacements and the frustration that poorly performing batteries
create. In most cases, the extra money invested is returned
because the batteries last longer and perform more efficiently.
 There
are two distinct varieties of chargers: the personal chargers
and the industrial chargers. The personal charger is sold
in attractive packaging and is offered with such products
as mobile phones, laptops and video cameras. These chargers
are economically priced and perform well when used for the
application intended. The personal charger offers moderate
charge times.
In comparison, the industrial charger is designed
for employee use and accommodates fleet batteries. These chargers
are built for repetitive use. Available for single or multi-bay
configurations, the industrial chargers are offered from the
original equipment manufacturer (OEM). In many instances,
the chargers can also be obtained from third party manufacturers.
While the OEM chargers meet basic requirements, third party
manufacturers often include special features, such as negative
pulse charging, discharge function for battery conditioning,
and state-of-charge (SoC) and state-of-health (SoH) indications.
Many third party manufacturers are prepared to build low quantities
of custom chargers. Other benefits third party suppliers can
offer include creative pricing and superior performance.
Not all third party charger manufacturers meet
the quality standards that the industry demands, The buyer
should be aware of possible quality and performance compromises
when purchasing these chargers at discount prices. Some units
may not be rugged enough to withstand repetitive use; others
may develop maintenance problems such as burned or broken
battery contacts.
Uncontrolled over-charge is another problem of
some chargers, especially those used to charge nickel-based
batteries. High temperature during charge and standby kills
batteries. Over-charging occurs when the charger keeps the
battery at a temperature that is warm to touch (body temperature)
while in ready condition.
 Some temperature rise cannot be avoided when charging
nickel-based batteries. A temperature peak is reached when
the battery approaches full charge. The temperature must moderate
when the ready light appears and the battery has switched
to trickle charge. The battery should eventually cool to room
temperature.
If the temperature does not drop and remains
above room temperature, the charger is performing incorrectly.
In such a case, the battery should be removed as soon as possible
after the ready light appears. Any prolonged trickle charging
will damage the battery. This caution applies especially to
the NiMH because it cannot absorb overcharge well. In fact,
a NiMH with high trickle charge could be cold to the touch
and still be in a damaging overcharge condition. Such a battery
would have a short service life.
A lithium-based battery should never get warm
in a charger. If this happens, the battery is faulty or the
charger is not functioning properly. Discontinue using this
battery and/or charger.
It is best to store batteries on a shelf and
apply a topping-charge before use rather than leaving the
pack in the charger for days. Even at a seemingly correct
trickle charge, nickel-based batteries produce a crystalline
formation (also referred to as ‘memory’) when left
in the charger. Because of relatively high self-discharge,
a topping charge is needed before use. Most Li-ion chargers
permit a battery to remain engaged without inflicting damage.
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