Technical data

Document No. 5-0324 Rev C
Page 13 of 21
E. Open Circuit Voltage: The battery state of charge can be determined
(approximately) from reading the battery’s open circuit voltage (OCV). To get an
accurate OCV, the battery needs to be stabilized on open circuit (no charging or
discharging current) for at least 4 hours. Once the stabilized OCV is measured,
the state of charge can be determined from the following table:
Table 2. State of Charge versus Open Circuit Voltage
Open Circuit Voltage
State of Charge (%)
12V Battery
24V Battery
12.9 or above
25.8 or above
100%
12.6
25.2
75%
12.3
24.6
50%
12.0
24.0
25%
11.7 or below
23.4 or below
0%
NOTE: THE BATTERY STATE OF CHARGE SHOULD NOT BE CONFUSED
WITH STATE OF HEALTH (SEE GLOSSARY). A BATTERY AT 100% STATE
OF CHARGE MAY OR MAY NOT HAVE GOOD STATE OF HEALTH (THAT IS,
THE ACTUAL CAPACITY MAY OR MAY NOT BE CONSIDERED
AIRWORTHY). THE ONLY RELIABLE METHOD TO DETERMINE BATTERY
STATE OF HEALTH IS BY CAPACITY TEST (SEE SERVICING SECTION).
F. Aircraft Storage: When an aircraft is placed in storage or remains dormant for an
extended time, it is best to disconnect the battery connector. This practice will
eliminate unnecessary drain on the battery if parasitic loads are present. Parasitic
loads can deplete battery capacity and result in battery sulfation (see Paragraph G).
G. Sulfated Batteries: Lead-acid batteries become sulfated when they remain in
a discharged state for extended periods of time. The longer the time period and
the greater the depth of discharge, the worse the sulfation becomes. Sulfation
may be reversible or irreversible, depending on the severity. Sulfation is
evidenced by a low open circuit voltage (below 12.5V for a 12 volt battery or 25.0
volts for a 24 volt battery) after the battery has been subjected to a full recharge
using normal (constant voltage) charging conditions. If the battery appears to be
sulfated, it should be removed from the aircraft and subjected to a capacity test
as detailed in the applicable CMM.
To prolong the battery service life, conditions leading to sulfation should be
prevented as much as possible. For example, if the master switch is inadvertently
left on and the battery becomes deeply discharged, it should be charged as soon
as possible. Another cause of sulfation is a parasitic load that drains the battery
capacity during extended dormant periods, as described in Paragraph F. Yet
another cause of sulfation is repetitive short duration flights that do not give
sufficient time for the battery to become fully charged. In this case, a periodic
maintenance charge should be included to assure the battery becomes fully
charged so as to minimize the buildup of sulfation.