Technical Manual

Document No. 6-0101 Rev. F Page 22 of 40
5.6 Deep Discharge Recovery
Batteries having an OCV less than 1.93 volts/cell (11.6 volts for a 12V battery) are considered
deeply discharged. This condition may occur when batteries are stored for long periods of time
without boost charging, or when discharged below 100% and not recharged. Batteries in this
condition may sometimes be recovered using a constant current charge instead of a constant
voltage charge. The deep discharge recovery procedure is given below.
WARNING: This procedure should only be done by a trained technician. Refer to Chapter
6 for safety precautions.
WARNING: This procedure should only be done in a well ventilated area because a
significant amount of hydrogen gases and fumes may be released from the battery.
CAUTION: If the battery becomes hot (above 55°C/130°F) during this charge, stop the
current and allow the battery to cool to room temperature before continuing.
1. Stabilize the battery at 20-30°C (68-86°F) for at least 24 hours.
2. Charge at a constant current of 5% of rated (24 hour) capacity until the voltage reaches
2.58 VPC (15.5 volts for a 12-volt battery), then continue charging at this rate for an additional 4
hours. Note that the charging voltage may get as high as 3.0 volts/cell, so the power supply
must be capable of outputting this level to maintain constant current. This constant current
charge may take 16 to 20 hours.
NOTE (1): If the battery voltage exceeds 2.58 volts/cell at the beginning of charge and
then drops below 2.58 volts/cell within 2 hours, continue charging at constant current
until the voltage reaches 2.58 volts/cell a second time. Then continue charging for an
additional 4 hours as specified above.
NOTE (2): If the battery voltage does not reach 2.58 volts/cell within 24 hours, the charge
should be terminated.
5.7 Capacity Testing
To determine the actual capacity of a Lifeline® AGM battery relative to its rated capacity, a full
discharge test should be performed. Although there are various battery testers available on the
market, such as carbon pile testers, impedance meters, conductance meters, and others, these
testers are not reliable in determining the battery’s actual capacity. To determine the battery’s
actual capacity relative to its rated capacity, use the following procedure:
1. Stabilize the battery at 68-86°F (20-30°C) for at least 24 hours.
2. Bring the battery to full charge as described in Sections 5.4, 5.5 or 5.6 as applicable.
3. Discharge the battery at a constant current of 25 amperes until the voltage falls to 10.5
volts (5.25 volts for a 6 Volt battery). Record the discharge time in minutes.
4. Compare the measured discharge time to the published 25A rating (reserve capacity
minutes) for the battery.
5. If the battery delivers less than 80% of the rated capacity the conditioning procedure
given in Section 5.5 should be attempted and the battery capacity should be retested.
6. If the battery delivers less than 50% of its rated capacity, it should be replaced.
However, the user should determine the amount of capacity needed for their particular
application and adjust the pass/fail threshold accordingly.