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9.3 Specific Gravity Check
Use a battery hydrometer to check the specific gravity of the electrolyte in each battery cell of batteries with filler caps. Holding
the hydrometer vertically, read the number on the glass bulb at the top of the electrolyte level or the number adjacent to the
pointer. If the hydrometer used does not have a correction table, consult Figure 16.
Figure 16 Specific Gravity Temperature Correction
Determine the specific gravity and electrolyte temperature of the battery cells. Locate the temperature in Figure 16 and correct
the specific gravity by the amount shown. The battery is fully charged if the specific gravity is 1.260 at an electrolyte temperature
of 26.7°C (80°F). Maintain the specific gravities between cells within ±0.01 of each other. Charge the battery if the specific gravity
is below 1.215 at an electrolyte temperature of 26.7°C (80°F).
Note:
Some battery testers have four or five beads in a test tube. Draw electrolyte into the tube as with the battery hydrometer described
in this section or use the manufacturer’s instructions. Use Figure 17 to interpret typical test results.
Example No. 1
Temperature below 26.7°C (80°F)
Hydrometer Reading 1.250
Acid Temperature - 6.7°C (20°F)
Subtract .024 Specific Gravity
Corrected Specific Gravity is 1.226
1.250 - .024 = 1.226
Example No. 2
Temperature above 26.7°C (80°F)
Hydrometer Reading 1.235
Acid Temperature 37.8°C (100°F)
Add .008 Specific Gravity
Corrected Specific Gravity is 1.243
1.235 + .008 = 1.243
The temperature correction amounts to about .004 (4 points) of
specific gravity for each 5.5°C (10°F) change in temperature.
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