MOTOR TRUCK SERVICE MANUALELECTRICAL
Precautions When Working Around Batteries
f a worn-out, corroded or undersize cable. Faulty battery
performance may indicate cable trouble.
It cannot be stressed too strongly that there are
PROPERTIES OF ELECTROLYTE
certain dangers involved in working with or around lead-
acid batteries. Care should be taken to avoid these
pecific Gravity Affects Freeze Point
Specific gravity of the electrolyte determines the
1. Electrolyte is a combination of water and sulfuric acid
temperature at which a battery will be harmed or
and as such is dangerous to clothing, vehicle parts
damaged by freezing.
and human skin-and especially dangerous to the
eyes. Take care to avoid slopping or spilling acid
Chart D which follows gives the freezing point of
battery electrolyte at given specific gravities.
on the skin should be washed off with cold water and
soap as soon as possible. Eyes should be
immediately washed with cold water and a physician
Electrolyte Specific Gravity
Freezing Point (F)
90° below 0°
75° below 0°
NOTE: Use only distilled water or odorless,
30° below 0°
colorless and tasteless drinking water in a storage
20° below 0°
battery. Patent electrolytes or battery dopes are
10° below 0°
injurious and void the battery guarantee.
10° above 0°
2. Never smoke or bring a flame close to batteries.
20 above 0°
The gas given off during charging is hydrogen, which
32° above 0°
is extremely explosive in the presence of a spark or
flame, Fig. 18. Never check the condition of a
battery by shorting between terminals, and for
safety's sake never lay tools or other metal objects
Temperature Affects Battery Capacity
on top of a battery where they might short between
terminals or short between ground and the
The battery container is a good heat insulator, and
ungrounded terminal. Always remember that one
the electrolyte temperature will lag several hours behind
side of the battery is grounded to the frame of the
vehicle and when working on other electrical
components, it is best to remove the ground side of
The specific gravity of the electrolyte (distilled water
the battery first.
and acid solution) must be maintained at 1.225
minimum, and the level of the solution should be at the
indicator level in the battery cover. A fully charged
battery has a specific gravity of 1.255- 1.270 at 80° F.
To eliminate the possibility of harmful sulfation of
plates, a battery with a specific gravity of 1.225 or less
should be recharged.
The following chart (E) shows the effect of
temperature on the capacity of a battery.
80° above 0°
60° above 0°
40° above 0°
20° above 0°
20° below 0°
Fig. 18 Explosion Caused by Open Flame Near Battery