Battery Basics
Introduction
As with anything technical, greater knowledge of the basics may help you
increase
performance, reliability, and
longevity,
as well as
prevent future problems with your batteries.
This article will provide information regarding your
coach
batteries; however,
this is
only one aspect of your coach's electrical system.
To learn more about
your batteries'
role
within the system, please refer to the
12 Volt Electrical
article.
Commercial lead acid batteries have been used for over 150 years.
The same chemical principal
used to store energy
now was also used
many generations ago.
Present day chassis battery power requirements are tremendous,
considering today's vehicles and all of the electrical devices that must be supplied.
All of these electronics require a
reliable power source, and poor battery condition may lead to
expensive electronic component failure.
A battery is like a
piggy bank - it stores energy, but cannot produce it.
If you continue to withdraw without making
any deposits, you will
soon have nothing left.
Life Span of a Battery
Not
long ago, motor homes only used
a single 12 Volt house battery.
Today, however, it is standard to have at least two
batteries, and up to 16 total in some
Newmar coaches,
powering inverters
up to 3000 watts.
As energy requirements
increase, the average battery life decreases.
The life span of a deep cycle battery will vary considerably with how it is
used, how it is maintained and charged, temperature, and other factors.
The life span is dependent upon
usage but
often
ranges between six
months to 48 months.
Only 30 percent
of all batteries actually reach the 48
month mark.
One simple way to extend battery life is to hook it up to a solar charger during the off months.
It is best practice to change the complete battery bank when a new battery becomes necessary, as
the battery bank is
only as good as the weakest
cell.
Common Battery Terms
Ampere (Amp) -
A unit that defines the flow rate of electricity (current) in a circuit.
Amp Hour (AH) -
Measurement of electrical storage capacity on a deep cycle battery.
The standard amp
rating is
taken
for 20 hours.
Example: A
100 AH rated battery is determined
like this: Draw from the battery for 20 hours
provides
a total of 100
amp
hours, translating
to about five
amps an hour
(5 amps x 20 hours = 100 AH).
However, it is important to know that
the
total time of discharge and load applied is not a linear relationship.
As your load increases, your realized capacity
decreases.
This means if you discharged that same 100 AH battery by a 100 amp load, it
will not
give you one hour of
runtime.
On the contrary, the perceived capacity of the battery will be about 64 AH.
Cold Cranking Amps (CCA) -
Measures
the number of amps a battery can deliver at 0° F for 30 seconds without
dropping below 7.2 Volts (1.2 Volts per cell).
A
high CCA battery rating is especially important in engine-starting battery
applications
and in cold weather.
This measurement is not particularly important in deep cycle batteries, though it is the
most commonly known
battery measurement.
Cranking Amps (CA) -
Measures available current at 32° F and is also called
marine cranking amps (MCA).
Depth of Discharge (DOD) -
Measures the percent of rated capacity to which a cell or battery is discharged.
It is the
reciprocal of a battery's state of charge.
Example: A battery that has a depth of discharge of 45 percent has a state of
charge of 55 percent.
Reserve Capacity (RC) -
Measures
the number of minutes a fully charged battery can continuously deliver 25 amps
at
80 ° F before the voltage drops below 10.5 Volts. This measurement represents the amount of time the battery can
operate if a charging system failure occurs.
Electrolyte Specific Gravity (battery test) -
Unit of measure which compares the
weight of the electrolyte solution to
the weight of water.
This test is performed with a hydometer
or a refractometer that is made for testing batteries.
This
type of test is used to determine the battery's state of charge; however, it cannot be used
on sealed batteries.
Battery Types
Liquid Lead Acid / Flooded
The Lead Acid battery consists of a plastic container with cells molded into it.
Each cell contains
plates, lead, and lead
oxide (various other elements are used to change density, hardness, porosity, etc.) with 35 percent
sulfuric acid and a
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