TM 10-6140-200-14
a. Low Temperatures. Available battery power is re-
1-9. Rated Capacity
duced by low temperature because electrolyte viscosity
The rated capacity of a storage battery is the number
and resistance is increased and diffusion throughout the
of ampere-hours or watt-hours which it is capable of
pores of the active material is retarded. For example, a
delivering when fully charged and under specified condi-
fully charged battery (1.275 to 1.295 specific gravity at
tions of temperature, rate of discharge, final voltage and
77 degrees F.), when its electrolyte temperature is about
specific gravity. United States industry standards for
32 degrees F., will deliver only 75% of the capacity which
motive power batteries always specify this to be at the 6
would be available at normal room temperature. This
drops to 40% at 0 degreee F. The electrolyte could freeze
hour rate of discharge. The total capacity available from a
battery is greatest at low rates of discharge over a long
if a discharged battery was exposed to very cold tempera-
tures for several hours. See Table 1-1 for freezing points
period of time. Discharging at high current rates reduces
of various electrolyte concentrations.
the total ampere-hours or watt-hours available.
Table 1-1. Freezing points of various
electrolyte concentrations
1-10. Sulfation
Standard Specific
This occurs when conditions within the cell cause
Freezing Point
State of
Gravity 1.275
sufficient accumulation of abnormal lead sulfate at both
(Degrees
Charge-Approx.
to 1.295
the positive and negative plates to permanently effect the
Fahrenheit)
(Percent)
Fully Charged
normal chemical reactions. Habitual overdischarging below
final voltage, prolonged operation in an undercharged
-95
1.280
100
condition and extended stand periods while in a dis-
1.250
-62
75
charged state are major causes of sulfation. A servicing
1.220
-31
50
schedule should be followed to provide frequent monitor-
+1
1.160
25
ing and adequate charging. See Chapter 3, Section 1 for
+10
1.130
10
methods of restoring a sulfated battery.
b. In addition to the discharge related problems, the
1-11. Operating Cycle
charge acceptance of a lead-acid battery is impaired when
electrolyte temperatures drop below 60 degrees F. As a
An operating cycle of a storage battery is the discharge
result, batteries should always be kept fully charged,
during use and subsequent charge to restore its initial
especially in cold weather. They should be heated, even
condition.
during operation or storage, if exposure is severe enough
to cause the temperature of the electrolyte to approach
32 degrees F.
1-12. Service Life
c. High Temperatures. Although high temperatures, up
The service life of a storage battery is the period
to 110 degrees F., do not cause a reduction in available
during which it provides useful power while being
capacity, battery operation is adversely effected. Because
discharged. It is usually expressed as the time period, or
most chemical reactions are accelerated at high tempera-
number of cycles, which elapses before the ampere-hour
tures, the rate of corrosion of the positive grid is
capacity falls below 80% of its rated value. To obtain
maximum service life it is recommended that a battery be
increased and the active material is shed more rapidly.
restricted to one full cycle per 24 hour day or fewer than
Even electrolyte temperatures above 90 degrees F. will
300 cycles per year. Other factors which most often
cause some reduction in service life and should be avoided
adversely influence service life are:
whenever possible. Cell temperatures should never be
allowed to exceed 110 degrees F.
d. In the past it was believed that, when batteries were
a. Abnormally high or low electrolyte temperatures.
to be used in the tropics, the specific gravity of the
b. Frequent overdischarging.
electrolyte should be reduced to approximately 1.225.
c. Failure to add water regularly.
The battery industry no longer recommends such action.
d. Frequent overcharging.
Any advantages which can be related to reducing the
e. Poor, or high, resistance, connections or contacts.
specific gravity are more than offset by the problems of
(1) electrolyte adjustment, (2) identifying such reduction
to all battery service personnel so the batteries are
1-13. Effect of Temperature
properly charged, (3) greater internal resistance, (4)
reduced cell capacity and (5) assuring that the higher
The normal operating characteristics of a storage
gravities are again restored if batteries are reshipped to a
battery are modified by unusually low or high cell
cold climate where freezing could be a problem.
temperatures.
1-7
