B
50
Repair and Service Manual
BATTERIES AND CHARGING
Read all of SAFETY and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
634756
can be done to salvage the battery; however, the individ-
ual battery should be replaced with a good battery of the
same brand, type and approximate age.
Hydrometer
A hydrometer (P/N 50900-G1) is used to test the state of
charge of a battery cell (Ref. Fig. 7). This is performed by
measuring the density of the electrolyte, which is accom-
plished by measuring the specific gravity of the electro-
lyte. The greater the concentration of sulfuric acid, the
more dense the electrolyte becomes. The higher the den-
sity, the higher the state of charge.
To prevent battery explosion that could result
in severe personal injury or death, never insert
a metal thermometer into a battery. Use a
hydrometer with a built in thermometer that is
designed for testing batteries.
Fig. 7 Hydrometer
Specific gravity is the measurement of a liquid that is
compared to a baseline. The baseline is water which is
assigned a base number of 1.000. The concentration of
sulfuric acid to water in a battery is 1.280 which means
that the electrolyte weighs 1.280 times the weight of the
same volume of water. A fully charged battery will test at
1.275 - 1.280 while a discharged battery will read in the
1.140 range.
.
Do not perform a hydrometer test on a battery that has
just been watered. The battery must go through at least
one charge and discharge cycle in order to permit the
water to adequately mix with the electrolyte.
The temperature of the electrolyte is important since the
hydrometer reading must be corrected to 80° F (27° C).
High quality hydrometers are equipped with an internal
thermometer that will measure the temperature of the
electrolyte and include a conversion scale to correct the
float reading. It is important to recognize that the electro-
lyte temperature is significantly different from the ambient
temperature if the vehicle has been operated.
Using A Hydrometer
1.
Draw electrolyte into the hydrometer several times to
permit the thermometer to adjust to the electrolyte
temperature and note the reading. Examine the color
of the electrolyte. A brown or gray coloration indi-
cates a problem with the battery and is a sign that
the battery is nearing the end of its life.
2.
Draw the minimum quantity of electrolyte into the
hydrometer to permit the float to float freely without
contacting the top or bottom of the cylinder.
3.
Hold the hydrometer in a vertical position at eye level
and note the reading where the electrolyte meets the
scale on the float.
4.
Add or subtract four points (.004) to the reading for
every 10° F (6°C) the electrolyte temperature is
above or below 80° F (27° C). Adjust the reading to
conform with the electrolyte temperature, e.g., if the
reading indicates a specific gravity of 1.250 and the
electrolyte temperature is 90° F (32° C),
add
four
points (.004) to the 1.250 which gives a corrected
reading of 1.254. Similarly if the temperature was 70°
F (21° C),
subtract
four points (.004) from the 1.250
to give a corrected reading of 1.246 (Ref. Fig. 8).
5.
Test each cell and note the readings (corrected to
80° F or 27° C). A variation of fifty points between
any two cell readings (example 1.250 - 1.200) indi-
cates a problem with the low reading cell(s).
As a battery ages the specific gravity of the electrolyte will
decrease at full charge. This is not a reason to replace
the battery, providing all cells are within fifty points of each
other.
Since the hydrometer test is in response to a vehicle
exhibiting a performance problem, recharge and repeat
32
28
24
20
16
12
8
4
0
4
8
12
16
20
24
28
32
36
32
28
24
20
16
12
8
4
0
4
8
12
16
20
24
28
32
36
1100
1125
1150
1200
1225
1250
1275
1300
1100
1125
1150
1200
1225
1250
1275
1300
Add to Float
Reading
Subtract
from Float
Reading
Bulb
Cylinder
Float
Weight
Thermometer
1175
