FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 2. Storage Batteries | 11-19. Battery Maintenance
AC 43.13-1B
9/8/98
hydrometer indication. As an example, a hy-
drometer reading of 1.260 and the temperature
of the electrolyte at 40 °F, the corrected spe-
cific gravity reading of the electrolyte is 1.244.
TABLE 11-2. Sulfuric acid temperature correction.
Electrolyte
Temperature
°C
°F
60
140
55
130
49
120
43
110
38
100
33
90
27
80
23
70
15
60
10
50
5
40
-2
30
-7
20
-13
10
-18
0
-23
-10
-28
-20
-35
-30
Points to be subtracted or added to
specific gravity readings
+24
+20
+16
+12
+8
+4
0
-4
-8
-12
-16
-20
-24
-28
-32
-36
-40
-44
11-19. BATTERY MAINTENANCE.
Battery inspection and maintenance procedures
vary with the type of chemical technology and
the type of physical construction. Always fol-
low the battery manufacturer’s approved pro-
cedures. Battery performance at any time in a
given application will depend upon the bat-
tery’s age, state of health, state of charge, and
mechanical integrity.
a. Age. To determine the life and age of
the battery, record the install date of the battery
on the battery. During normal battery mainte-
nance, battery age must be documented either
in the aircraft maintenance log or in the shop
maintenance log.
b. State of Health. Lead-acid battery
state of health may be determined by duration
of service interval (in the case of vented bat-
teries), by environmental factors (such as ex-
cessive heat or cold), and by observed electro-
lyte leakage (as evidenced by corrosion of
wiring and connectors or accumulation of
powdered salts). If the battery needs to be re-
filled often, with no evidence of external leak-
age, this may indicate a poor state of the bat-
tery, the battery charging system, or an over
charge condition.
(1) Use a hydrometer to determine the
specific gravity of the battery electrolyte,
which is the weight of the electrolyte com-
pared to the weight of pure water.
(2) Take care to ensure the electrolyte is
returned to the cell from which it was ex-
tracted. When a specific gravity difference
of 0.050 or more exists between cells of a bat-
tery, the battery is approaching the end of its
useful life and replacement should be consid-
ered. Electrolyte level may be adjusted by the
addition of distilled water.
c. State of Charge. Battery state of
charge will be determined by the cumulative
effect of charging and discharging the battery.
In a normal electrical charging system the bat-
tery’s generator or alternator restores a battery
to full charge during a flight of one hour to
ninety minutes.
d. Mechanical Integrity. Proper me-
chanical integrity involves the absence of any
physical damage as well as assurance that
hardware is correctly installed and the battery
is properly connected. Battery and battery
compartment venting system tubes, nipples
and attachments, when required, provide a
means of avoiding the potential buildup of ex-
plosive gases, and should be checked periodi-
cally to ensure that they are securely connected
and oriented in accordance with the mainte-
nance manual’s installation procedures. Al-
ways follow procedures approved for the spe-
cific aircraft and battery system to ensure that
the battery system is capable of delivering
specified performance.
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