Battery Care and Feeding.
Common rechargeable batteries are generally one
of four types. These are lithium ion, nickel
metal hydride, nickel cadmium, or sealed lead
acid. Within each type there are subtypes. For
example, nickel cadium batteries (NiCads) exist
in sintered cell and pocket cell types. Sealed lead
Acid batteries exist in gell cell and absorbent
glass mat. These different types of batteries
have different characteristics which gives them
more or less suitability for a given application.
One of these characteristics is most closely
associated with the NiCads. This is known as the
"memory effect". A NiCad cell will "remember" how
full it is charged and how deeply it is discharged
and will not want to go past those points without
a large drop in voltage. This makes it seem like
the battery will not hold a charge in some
applications. To get around this, some battery and
appliance manufacturers recommend completely discharging
and then fully recharging a NiCad battery so it "remembers"
a full cycle.
Sealed Lead Acid batteries should not
be run all the way down because it can cause the plates
to sulfate and quickly kill the battery. These should
generally be kept fully charged and be charged at the
earliest opportunity after discharging them. Be careful not
to overcharge sealed batteries, as the seal will burst and
the liquid will evaporate ruining the battery in a short time.
Each type of battery has slightly different voltage
characteristics.
DEEP CYCLE BATTERIES:
The type of battery used for providing power in RE applications
is known as a "deep cycle" battery. True deep cycle batteries
have heavy duty plates and generally weigh over one hundred
pounds for twelve volts worth of cells. These come in all the
same flavors as the home flashlight batteries, but because of
their weight they are not very portable. They are also designed
to store a lot of energy to provide for extended periods of
discharge. A regular lead acid car battery is designed for
very "shallow" discharge cycles in which the user drains less
than twenty percent of the battery's energy before driving the
car and recharging the battery. Draining over fifty percent of
the energy out of one of these starting batteries will cause
permanent irreversible damage to the plates.
Deep cycle batteries are designed for
discharging hundreds or thousands of times to the fifty
percent level. Below the fifty percent level, voltage starts
dropping a lot and "sulfation" can start to decrease the
battery capacity of lead acid batteries. Equalization
charges are often done with lead acid batteries to
equalize the voltages and acid levels in the cells. In an
equalization charge, the battery is filled to overflowing
by continuing to charge it even after it is topped off.
This causes bubbling from the hydrogen gas being produced,
so ventilation is required to prevent an explosive condition
from arising.
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