TM 5-3805-255-14
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ELECTRICAL SYSTEM CONTINUED
Common Causes of Battery Failure
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1. Check these common causes first:
a. Resistance in the charging circuit.
b. Defective alternator or slipping alternator drive belt.
c.
Improper regulator adjustment, or faulty regulator.
d. Overload due to defective starting system, or excessive use of accessories.
e. Dirt and electrolyte on top of battery causing a constant drain.
f.
Hardened battery plates, commonly called "sulfation," due to the battery being in a low state of charge over
a period of time.
g. Physical defects such as shorted cells, loss of active material from the plates, warped plates, broken
terminals, etc.
2. It is important to note that, of the seven common causes of battery failure listed, the first five causes are
outside the battery. Any one of these conditions will result in a battery being at less than normal state of
charge.
3. The sixth cause listed can result from any one of the first five causes. That is, sulfation occurs when any
condition causes the battery to be undercharged for long periods of time. When a battery becomes sulfated, it
will not accept a normal rate of charge and also, its capacity decreases. Sulfation can usually be overcome by
prolonged slow charging or by discharging the battery completely, letting it stand discharged for 6 to 12 hours,
and then recharging it slowly.
4. The causes of battery failure listed last are the defects that can occur in the battery itself. If shorted cells or loss
of active material from the plates occurs when the battery has been in service for less than its guaranteed life,
it is usually a result of overworking or overcharging of the battery. Cracked cases, broken terminals, and
shorted cells can be caused by improper handling of the battery or a faulty battery carrier.
Freezing Points of Electrolyte
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The electrolyte of a battery will start to freeze (first ice crystals begin to appear in the electrolyte although it does
not freeze solid until a lower temperature is reached) approximately as indicated below (specific gravity readings
corrected to 80F).
1.280 sp. gr.................... Freezes at -90F (-68C)
1.250 sp. gr.................... Freezes at -62F (-52C)
1.200 sp. gr.................... Freezes at -16F (-27C)
1.150 sp. gr.................... Freezes at +15F (-9C)
1.100 sp. gr.................... Freezes at +19F (-7C)
Effect of Low Temperatures on Battery Performance
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Battery capacity is greatly reduced by cold, as cold has a decided numbing effect on the electro-chemical action in
the battery. The following comparison indicates the reduction in cranking power of a fully charged battery when the
temperature of the electrolyte drops from 80F (27C) to 32F (0C) and to 0F (-18C).
80F (27C)
100%
32F (0C)
65%
0F (-18C)
40%
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