Charging Methods & Applications of SLA Batteries

Application Charging Method Normal charging in 6 or more hours; Constant voltage control Two steps constant voltage control Constant Current Control
Cycle use Control voltage 7.25 to 7.45V /6V battery 14.5 to 14.9V/12V battery initial current 0.4CA or smaller.
Trickle use Control voltage 6.8 to 6.9/6V battery 13.6 to 13.8V/12V battery Initial charging with current of approx. 0.15CA, followed by switching voltage to trickle charge
Float use Control voltage 6.8 to 6.9/6V battery 13.6 to 13.8V/12V battery Float charging compensates for load fluctuations.
Refresh charge (Auxiliary charge)* When charging two or more batteries at a time, select only those which have been left under the same condition. Charging with current of approx. 0.1CA
Application example General uses, Cellular phones (bag phones), UPS, Lanterns, Electric tools. Medical equipment, Personal radios
Note: Refresh (auxiliary) charge amount should be 120% to 130% of self-discharge amount. For details, please contact us.

Precautions on charging

  1. (A) in constant voltage charging (cycle use): Initial current should be 0.3CA or smaller (C: rated capacity)
    (B) in V-taper charge control system: Initial current should be 0.6CA or smaller (C: rated capacity)
    (C) in constant voltage charging (trickle use): Initial current should be 0.15CA or smaller (C: rated capacity)

  2. Relation between standard voltage value in constant voltage charging and temperature is given in the table
    Relation between standard voltage in constant voltage charging and temperature
0°C 5°C 40°C
Cycle use 4V 5.1 4.9 4.7
6V 7.7 4.7 7.1
8V 10.2 9.8 9.5
12V 15.4 14.7 14.2
Trickle Use 4V 4.7 4.6 4.5
6V 7.1 6.8 6.7
8V 9.4 9.1 8.9
12V 14.1 13.7 13.4
  • (D) Discharge current
    Discharge capability of the 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 (1/20CA to 3CA): discharge beyond this range may result in marked decrease of discharge capacity or reduction in the number of times of repeatable discharge. When discharging the battery beyond said range, please consult in advance.
  • (E) Depth of discharge
    Depth of discharge is the state of discharge of batteries expressed by ratio of amount of capacity discharge to the rated capacity.


  • (A) Observe the following condition when the battery needs to be stored.
    • (1) Ambient temperature: -15°C to 40°C(preferably below 30°C).
    • (2) Relative humidity: 25 to 85%
    • (3) Storage place free from vibration, dust, direct sunlight, and moisture.

  • (B) 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 the capacity, repeat charge/discharge several times for the battery in cycle use, continue charging the batter as loaded in the equipment for 48 to 72 hours.

  • (C) 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 on depending ambient temperature. Avoid storing the battery for more than 12 months.

Storage temperature Interval of auxiliary charge(refresh charge)
Below 20°C 9 months
20°C to 30°C 6 months
30°C to 40°C 3 months
  • (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 the storage. The higher the ambient temperature, the less the residual capacity after storage for a specific period. Self discharge rate almost doubles by each 10°C rise storage temperature.

  • Residual capacity test result

  • (E) Open circuit voltage vs. Residual capacity
    Residual capacity of the battery can be roughly estimated by measuring the open circuit voltage as shown in the figure.

    Open circuit voltage vs. Residual capacity 25°C

  • Temperature conditions
  • Recommended temperature ranges for charging, discharging and storing the battery are tabulated below.

Charge temperature 0°C to 40°C
Discharge -10°C to 60°C
Storage -10°C to 40°C

Battery Life

  • (A) Cycle life
    • Cycle life (numbers of cycles) of the battery is dependent on the depth of discharge in each cycle. The deeper the discharge is, the shorter the cycle life (smaller number of cycles), providing the same discharge current. The cyclic life (number of cycles) of the battery is also related to such factors as the type of the battery, charge method, ambient temperature, and rest period between charge and discharge. Typical cycle-life characteristics of the battery by different charge/discharge conditions are shown by the below figures. This data is typical and tested at a well equipped laboratory. Cycle times are different for each battery model. Cycle times are also different from this data when using batteries under real conditions.

Cycle life vs. Depth discharge

Constant-voltage cycle life characteristics
Rapid-charge cycle life characteristics
Influence of temperature on trickle life
Trickle life characteristics at 50°C

Trickle (Float) Life Characteristics

Valve (One Way Valve)

If the internal pressure of the battery is raised to an abnormal level, the rubber one-way valve opens to release excessive pressure; thus the vent protects the battery from danger of bursting. Since the rubber valve is instantly resealable, the valve can perform its function repeatedly whenever required.

Example of Valve Construction

Terminal Type

About Power Rite Batteries

  • All standard sizes offered from 6V, 2.3 Ah to 12V, 100 Ah.
  • Absorbed Glass Mat (AGM) design for long, trouble free life.
  • Meets or exceeds OEM requirements for use in emergency lighting and alarm systems.
  • Underwriters Laboratories recognized lead acid standby batteries.
  • Non-spillable sealed battery tested for safe transportation.


Phone: (877) 797-7483