7
Distilled or de-ionized water should only be added to
batteries while the batteries are on charge and gassing or as
soon after recharge as possible. This will prevent overfilling
because the electrolyte is at its maximum level during this time.
To prevent low electrolyte levels, frequent checks should be
made and water should be added when necessary.
How a watering schedule is determined depends on the type
of battery, frequency of charge, temperature of the battery, and
age and condition of the battery. Excessive water loss may be
caused by shorted or weakened cells, excessive charging rates,
or the charger not shutting off automatically. Cells that contin-
ually lose excessive amounts of water should be checked for
possible internal damage.
Performing a Test Discharge
To determine if a battery can deliver its rated capacity, a test
discharge, or capacity test, can be performed. This test helps
determine the “health” of a battery and whether or not it should
be replaced.
Only experienced battery technicians should be allowed
to prepare a battery for discharge testing and to conduct the
actual discharge test.
The test is conducted by discharging a fully charged battery at a
specific rate until the battery voltage drops to a predetermined
volts per cell, times the number of cells in the battery.
By noting the time elapsed between when the battery was put
on discharge and when the final voltage was reached, you can
determine whether the battery is delivering its rated capacity:
1. Give the battery an equalizing charge and adjust the
specific gravity to the manufacturer’s specification, with the
electrolyte level at the bottom of the vent well. Always tem-
perature correct the gravity readings.
2. Start the test and record the starting time.
3. Record battery voltages during the first hour at
10 minutes, 30 minutes and then 60 minutes. After
the first hour, take hourly readings until the first battery
voltage reaches 1.80 volts per cell. From this point on, re-
cord the voltage of the batteries every 5 minutes.
4. Carefully monitor the voltage of the low batteries and as the
voltage of each battery drops below the predetermined final
voltage, record the time.
5. When the majority of the battery reach termination value, stop
the test. Don’t let any battery go into reversal.
For example, if the test was run at the 360 minute rate was
terminated after 336 minutes; the capacity percentage would
be 93%
6. After termination of the test, immediately record the specific
gravity of each cell. If all the cells have uniform specific gravity
and the battery delivers 50% or more of its rated capacity, it
can be returned to service. If the test indicates that less than
50% of the battery’s rated capacity is being delivered, the bat-
tery should be either repaired or replaced, depending upon its
age and overall condition.
For more detailed information on capacity testing, contact
East Penn Manufacturing Company or your local authorized
East Penn Representative.
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