TP-5631 7/96
Scheduled Maintenance 3-5
Checking Specific Gravity
It is not possible to check the specific gravity of a
maintenance free battery. Use a battery hydrometer to
check the specific gravity of the electrolyte in each
battery cell. While holding the hydrometer vertical, read
the number on the glass bulb at the top of the electrolyte
level. Use the correction table in Figure 3-3 if the
hydrometer used does not have a correction table.
Determine specific gravity and electrolyte temperature
of battery cells. Locate temperature in Figure 3-3 and
adjust specific gravity by amount shown. The battery is
fully charged if the specific gravity is 1.260 at an
electrolyte temperature of 80
°
F (26.7
°
C).
The
difference between specific gravities of each cell should
not exceed
±
0.01. The battery should be charged if the
specific gravity is below 1.215 at an electrolyte
temperature of 80
°
F (26.7
°
C).
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
- 12.2
- 6.7
- 1.1
4.4
10
21.1
26.7
32.2
37.8
43.3
48.9
54.4
60.0
65.6
71.1
15.6
+ .032
+ .030
+ .028
+ .026
+ .024
+ .022
+ .020
+ .018
+ .016
+ .014
+ .012
+ .010
+ .008
+ .006
+ .004
+ .002
0
- .002
- .004
-. 006
- .008
- .010
- .012
- .014
- .016
- .018
- .020
- .022
- .024
- .026
- .028
°
C
°
F
EXAMPLE NO. 1
Temperature below 80
°
F
(26.7
°
C)
Hydrometer Reading 1.250
Acid
Temperature
20
°
F
(-6.7
°
C)
Subtract .024 Sp. Gravity
Corrected Sp. Gravity is 1.226
EXAMPLE NO. 2
Temperature
above
80
°
F
(26.7
°
C)
Hydrometer Reading 1.235
Acid
Temperature
100
°
F
(37.8
°
C)
Add .008 Sp. Gravity
Corrected Specific Gravity is
1.243
The temperature correction amounts to about .004 (4 points) of
specific gravity for each 10
°
F (5.5
°
C) change in temperature.
Correction
Figure 3-3. Specific Gravity Temperature
Correction
