During the mid 1970s, researchers developed a maintenance-free lead acid battery, which could operate in virtually any position. The

liquid electrolyte was transformed into moistened separators and the enclosure was sealed. 

Safety valves were added to allow venting of gas during charge and discharge.

Driven by diverse applications, two desigs of batteries emerged. They are the sealed lead acid battery (SLA), also known under the brand name of Gelcell, and the valve regulated lead acid (VRLA). Technically, both batteries are the same. There is no definative as to when a Sealed Lead Acid Battery becomes a VRLA. (It may be argued that there is no such battery as a sealed lead acid battery " as no lead acid battery can be totally sealed.  They are all are valve regulated.)

Sealed Lead Acid Batteries have a typical capacity range of 0.2Ah to 30Ah and powers portable and wheeled applications. Typical uses are personal UPS units for PC backup, small emergency lighting units either free standing or found in ceiling voids, ventilators for health care patients and wheelchairs. Because of low cost, dependable service and minimal maintenance requirements, the Sealed Lead Acid battery is often the preferred choice for health care instruments in hospitals and retirement homes.

The VRLA battery is generally used for stationary applications. Their capacities range from 30Ah to several thousand Ah and are found in larger UPS systems for power backup.

Flange Battery pack can be built in series and parallel configurations depending on whether you need maximum Voltage or increased Amp Hour

VRLA battery packs achieve the desired operating voltage by connecting several cells in series, with each cell adding to the total terminal voltage. Parallel connection attains higher capacity for increased current handling, as each cell adds to the total current handling. Some packs may have a combination of serial and parallel connections

Typical uses are cable distribution centres, Internet hubs, Wind turbines and utilities, as well as power backup for banks, hospitals, airports and military installations.

Unlike the flooded lead acid battery ( Wet Lead Acid ), both the Sealed Lead Acid and VRLA are designed with a low over-voltage potential to prohibit the battery from reaching its gas-generating potential during charge.

Excess charging would cause gassing and water depletion. Consequently, the Sealed Lead Acid and VRLA can never be charged to their full potential.

Among modern rechargeable batteries, the lead acid battery has the lowest energy density. For the purpose of analysis, we use the term "sealed lead acid" to describe the lead acid batteries for portable use and valve regulated lead acid for stationary applications. Because of our focus on portable batteries, we focus mainly on the Sealed Lead Acid Battery.

The Sealed Lead Acid Battery does not lend itself to fast charging - typical charge times are 8 to 16 hours. The SLA must always be stored in a charged state.

Leaving the battery in a discharged condition causes sulfation, a condition that makes the battery difficult, if not impossible, to recharge. Sealed Lead Acid Batteries are not subject to memory. Leaving the battery on float charge for a prolonged time does not cause damage. The battery's charge retention is best among rechargeable batteries. Whereas the NiCd self-discharges approximately 40 percent of its stored energy in three months, the Sealed Lead Acid Battery self-discharges the same amount in one year. The Sealed Lead Acid Battery is relatively inexpensive to purchase but the operational costs can be more expensive than the NiCd if full cycles are required on a repetitive basis.

Unlike the NiCd, the SLA does not like deep cycling. A full discharge causes extra strain and each discharge/charge cycle robs the battery of a small amount of capacity. This loss is very small while the battery is in good operating condition, but becomes more acute once the performance drops below 80 percent of its nominal capacity. This wear-down characteristic also applies to other battery chemistries in varying degrees. To prevent the battery from being stressed through repetitive deep discharge, a larger SLA battery is recommended. Depending on the depth of discharge and operating temperature, the SLA provides 200 to 300 discharge/charge cycles. 

 The optimum operating temperature for a VRLA battery is 25°C (77°F). Roughly every 8°C (15°F) rise in temperature will cut the battery life in half. 

Advantages and Disadvantages of Sealed Lead Acid Batteries


  • Cannot be stored in a discharged condition.
  • Low energy density - poor weight-to-energy density limits use to stationary and wheeled applications.
  • Allows only a limited number of full discharge cycles - well suited for standby applications that require only occasional deep discharges.
  • Environmentally unfriendly - due to the use of the electrolyte and the lead.
  • Transportation restrictions on flooded lead acid - there are environmental concerns regarding spillage in case of an accident.


  • Inexpensive and simple to manufacture - in terms of cost per watt hours, the SLA is the least expensive.
  • Reliable and well-understood technology - when used correctly, the SLA is durable and provides dependable service.
  • Low self-discharge - the self-discharge rate is among the lowest in rechargeable battery systems. 
  • Low maintenance requirements - no memory; no electrolyte to fill.
  • Capable of high discharge rates.
  • Speak to the sales team at CAB to discuss our full range of VRLA's.

VRLA Flexi - Products table & Filter

CAB Part
ChemistryDescriptionCell SizeDimensions (mm)Weight
14-260VRLA2 × NP6-12 VRLA41001212More info
14-262VRLA4 × NP4-6 VRLA3480186More info
14-263VRLA3 × NP4-6 VRLA2610126More info
14-305VRLA3 × NP12-3.2 Ah VRLA28503.212More info

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All our battery packs and products are made in purpose built facility in Great Britain.

Under the Waste Batteries and Accumulators Regulations 2009, CAB Special Batteries Ltd are a ‘Producer’ of ‘Industrial’ batteries and as such, are obliged to...

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CAB SPECIAL BATTERIES is proud to announce that they have been appointed as the GP Batteries uk and European “SUPER VALUE ADDED RE-SELLER”

Where safety is involved there should be no compromise. Cells used for this important application should be of the highest quality and performance.

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