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Battery Types
Starting Batteries:
Starting batteries are designed for high output cranking power, but not for deep cycling like the house batteries
are designed to do. Starting batteries will not last long in deep cycle application. The way they are rated should
give a good indication of their intended use. “Cold Cranking Amps” is a measurement of amperage output that
can be sustained for 30 seconds. Starting batteries use thin plates to maximize the surface area of the battery. This
allows a very high starting current but lets the plates warp when the battery is deep cycled (discharged).
Deep Cycle Batteries:
Deep cycle batteries are available in many sizes and types. The most common type is a non-sealed, liquid
electrolyte with battery caps. These caps should be removed periodically to check the level of electrolyte. When
a cell is low, only distilled water should be added. Water consumption will vary depending on many factors: how
far the batteries are depleted, how long the voltage is being applied to charge the batteries, how much voltage
is used and how often this occurs. Generally, the batteries should be checked every two or three weeks when
continuously hooked to shore power.
NOTE:
Tap water contains minerals which can alter battery chemistry and ruin the battery.
Use only distilled water when refilling the battery.
NOTE:
Discharging the battery past 50% capacity (State of Charge) can shorten the life of
the batteries.
Testing the Batteries
There are several ways that a battery can be tested and monitored.
The motorhome uses a systems panel that shows the status of the
batteries at a quick glance. Press and hold the test switch to display
the desired battery bank voltage. The most efficient way of testing the
batteries is to check the electrolyte solution with a battery hydrometer.
Hydrometers can be purchased from most auto parts stores.
Many styles are available, from types with cylinder graduation
(shown here) to types with floating balls. The hydrometer tests
the battery’s electrolyte solution which is measured in specific
gravity. Distilled water has a specific assigned gravity of 1,000.
The hydrometer is calibrated to this mark. Pure sulfuric acid has a
specific gravity reading of 1,840. The acid is 1.84 times heavier than
water. The electrolyte solution is about 64% water to 36% acid with
the battery fully charged. Hydrometers with cylinder graduation are
graphed and the exact state of specific gravity can be determined. A
fully charged battery will have a specific gravity reading of 1265 at 80º F.
Temperature and recent battery activity (charging or discharging) affect the hydrometer readings. It is best to
check the battery when it has been at rest for at least three hours, although readings taken at other times will
give a “ballpark” figure. When using the hydrometer, draw the electrolyte solution up into the tube. Allow the
hydrometer to attain the same temperature as the electrolyte solution. Note the reading for that cell. Complete the
same test for the rest of the cells on that battery bank. The hydrometer is calibrated at 80° F. Temperature affects
the hydrometer readings. The higher the electrolyte temperature, the higher the specific gravity reading. The lower
the temperature, the lower the specific gravity reading. Add or subtract four points for each 10° variance from the
80° F chart. Readings between cells should not vary more than 50 points.
020034c
030816
Battery hydrometer
