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.
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. One simple way to extend battery life is to hook it up to a solar charger during the off
months.
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
65 percent water solution. This solution is called an electrolyte, which causes a chemical reaction that releases
electrons.
When testing a battery with a hydrometer, the amount of sulfuric acid in the electrolyte is measured. If the reading is low,
the chemistry that makes electrons is lacking. The sulfur is now resting on the battery plates and will remain there until
the battery is recharged and the sulfur returns to the electrolyte.
ABSORBED GLASS MAT (AGM) / DRY CELL
The Absorbed Glass Mat battery is just like a flooded battery, except the electricity is maintained in the glass mats, as
opposed to freely flooding the plates. Very thin fibers are woven into a mat to increase the surface area to hold sufficient
electrolyte on the cells for their lifetime. The construction allows the electrolyte to remain suspended in close proximity
with the plate's active material, enhancing both the discharge and recharge efficiency.
When Deep Cycle AGM batteries are not discharged more than 60 percent, the cycle life could be approximately a few
hundred cycles. If you do not use or operate your equipment daily, AGM batteries will hold their charge better than most
other types. In most cases AGM batteries will provide a greater life span and cycle life than a Wet Cell battery.
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