CHARACTERISTICS - CONTINUED
d) Discharge current Discharge capability of batteries is expressed by the 20 hour rate (rated capacity). Select the battery for specific equipment so that the discharge current during use of the equipment falls within the range between 1/20 of the 20 hour rate value and 3 times that (1/20 CA to 3 CA): discharging beyond this range may result in a marked decrease of discharge capacity or reduction in the number of times of repeatable discharge. When discharging the battery beyond said range, please consult Panasonic in advance. (Note) With some types of SLA batteries which have a built-in thermostat, the thermostat may auto- matically cut off the circuit when discharge current exceeds 4 A at the ambient temperature of 40C; therefore, the maximum discharge current value should be the smaller one of either 4 A or 2 CA.
Depth of discharge Depth of discharge is the state of discharge of batteries expressed by the ratio of amount of capacity discharged to the rated capacity.
Observe the following condition when the battery needs to be stored.
Ambient temperature: -15C to 40C (preferably below 30C)
Relative humidity: 25 to 85%
Storage place free from vibration, dust, direct sunlight, and moisture.
Self discharge and refresh charge During storage, batteries gradually lose their capacity due to self discharge, therefore the capacity after storage is lower than the initial capacity. For the recovery of capacity, repeat charge/discharge several times for the battery in cycle use; for the battery in trickle use, continue charging the battery as loaded in the equipment for 48 to 72 hours.
Refresh charge (Auxiliary charge)
When it is unavoidable to store the battery for 3 months or longer, periodically recharge the battery at the intervals recommended in the table below depending on ambient temperature. Avoid storing the battery for more than 12 months.
Interval of auxiliary charge (refresh charge)
20C to 30C
30C to 40C
d) Residual capacity after storage The result of testing the residual capacity of the battery which, after fully charged, has been left standing in the open- circuit state for a specific period at a specific ambient temperature is shown in the figure below. The self discharge rate is very much dependent on the ambient temperature of storage. The higher the ambient temperature, the less the residual capacity after storage for a specific period. Self discharge rate almost doubles by each 10C rise of storage temperature.
Residual capacity test result
69 Storage period (months)
Sealed Lead-Acid Handbook, Page 17