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The ‘Green Light’ Lies
When charging a battery, the ready light will
eventually illuminate, indicating that the battery is fully
charged. The user assumes that the battery has reached its
full potential and the battery is taken in confidence.
In no way does the ‘green light’ guarantee sufficient
battery capacity or assure good state-of-health (SoH). Similar
to a toaster that pops up the bread when brown (or black),
the charger fills the battery with energy and ‘pops’ it to
ready when full (or warm).
The rechargeable battery is a corrosive device
that gradually loses its ability to hold a charge. Many users
in an organization are unaware that their fleet batteries
barely last a day with no reserve energy to spare. In fact,
weak batteries can hide comfortably because little demand
is placed on them in a routine day. The situation changes
when full performance is required during an emergency. Total
collapse of portable systems is common and such breakdowns
are frequently related to poor battery performance. Figure 11-1
shows five batteries in various states of degradation.
Figure 11-1: Progressive loss of charge
acceptance.
The rechargeable battery is a corrosive
device that gradually loses its ability to hold charge as
part of natural aging, incorrect use and/or lack of maintenance.
The unusable part of the battery that creeps in is referred
to as ‘rock content’.
Carrying larger packs or switching to higher
energy-dense chemistries does not assure better reliability
if the weak batteries are not ‘weeded’ out at the appropriate
time. Likewise, the benefit of using ultra-advanced battery
systems offers little advantage if packs are allowed to remain
in the fleet once their performance has dropped below an acceptable
performance level.
Figure 11-2 illustrates four
batteries with different ratings and SoH conditions. Batteries
B, C and D show reduced performance because of memory problems
and other deficiencies. The worst pack is Battery D. Because
of its low charge acceptance, this battery might switch to
ready after only 14 minutes of charge (assumed time).
Ironically, this battery is a likely candidate to be picked
when a fresh battery is required in a hurry. Unfortunately,
it will last only for a brief moment. Battery A, on the other
hand, has the highest capacity and takes the longest to charge.
Because the ready light is not yet lit, this battery is least
likely picked.
Figure 11-2: Comparison of charge and
discharge times.
This illustration shows typical
charge and discharge times for batteries with different ratings
and SoH conditions. Carrying larger batteries or switching
to high energy-dense chemistries does not necessarily assure
longer runtime if deadwood is allowed to remain in the battery
fleet.
 The weak batteries are charged quicker and remain on ‘ready’
longer than the strong ones. The bad batteries tend to gravitate
to the top. They become a target for the unsuspecting user.
In an emergency situation that demands quick charge action,
the batteries that show ready may simply be those that are
deadwood.
A weak battery can be compared to a fuel tank
with an indentation. Refueling this tank is quicker than a
normal tank because it holds less fuel. Similar to the ‘green
light’ on a charger, the fuel gauge in the vehicle will show
full when filled to the brim, but the distance traveled before
refueling will be short.
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