Rolls VRLA sealed OPzV GEL batteries have very similar installation and maintenance requirements as Rolls sealed AGM product lines, with the exception of unique charge and float voltages. Although they are a sealed battery, ventilation is still required to avoid risk of off-gassing and explosion and general battery cleaning and maintenance should be followed.  For more information, please refer to the Rolls Battery User Manual


NOTE: Use the highlighted voltage set points when charge equipment is supplied with a temperature sensor. Set at 3mV/ºC/Cell...(+/- 72mV per ºC from a 25ºC Delta  - 48V System) Higher or lower settings may cause incorrect adjustments in charg e voltage. Without a temperature sensor, charge settings must be adjusted manuall y based on the battery temperature when in use, not just ambient temperatures.

NOTE: The ideal float voltage is the lowest voltage setting that will maintain the battery at full charge. 

Rebulk Voltage:  This setting determines the battery bank voltage may drop between a Float and Bulk charge.  It may be set at personal preference.  For assistance and recommendation, please refer to the charge controller manufacturer for instruction and detailed information on this setting.


Absorption Time:

The most important part of the charge cycle is the Absorption charge.  The Bulk charge phase recharges the battery bank to an 80% level.  The Absorption charge phase completes the charging cycle, during which charge resistance increases. Most chargers on the market have a timer that allows the user to adjust the duration for the required time to return the battery to full charge. To set the correct time, a simple calculation is used.  With the help of the 20 AH capacity and charge current, you may calculate the remaining charge time required for the battery bank to reach 100% state of charge (SOC) using the following equation:

We recommend a charge current of 20% of the 20 hr rate for both Bulk & Absorption charge phases on AGM & GEL VRLA models.

Often, OPzV GEL batteries are used in grid-connected backup applications where charge times are not limited to a renewable charge sources.  In these situations, a charge rate of 10% is acceptable.  A charge rate of 20% is ideal where charge time is limited and reaching 100% SOC must be achieved in a shorter timeframe - ex: solar.

[10% min, 20% recommended, 30% max]

t = 0.38 x (C/I)


t = Absorption Charge Time (Hours)

C = 20 hr Rated Capacity (AH)                [ex: 1 string x S2-690GEL models (785AH)  =  AH rated capacity]

I = Charging Current (Amps)                  [charger output min 10% up to max 30% of 20 hr rate]   


1 string of S2-690GEL batteries

20 hr rate = 785 AH

I =20% of 785 AH = 157 Amps    OR      If the charger output is limited to 120 Amps max then 120 is used

T = 0.38 x 785/157 = 1.9 hrs      
OR      T = 0.38 x 785/120 = 2.49 hrs