VRLA Battery General Knowledge

  • What's VRLA battery

  • Typical VRLA battery applications

  • Size of battery

  • Charging

  • Battery Storage, Care & Maintenance

  • VRLA Battery Safety

  • Battery recycling

  • Glossary

What's VRLA battery

A battery is an electricity storage device which can be found in any number of shapes, size, voltage and capacities.

When two conducting materials (often dissimilar metals) are immersed in a solution, an electrical potential will exist between them is connected together through a closed circuit, a current will flow. The value of this potential (or voltage) is dependent on the materials used, giving rise to a whole family of battery types each having benefits and restrictions in use. Examples are: – lead acid, nickel cadmium ( NiCad ), lithium, silver alkaline.

This manual is concerned only with one battery technology, the most successful «Lead Acid battery» (lead and lead oxide immersed in sulphuric acid). Each cell has a 2 volt potential.

The Lead-acid Battery

A battery is simply a number of cells connected together with a given voltage and capacity. The more cells the higher the voltage, the large the plates the higher the capacity (in general).

Purely for convenience, batteries are made in 12 volt blocks with 6 cells but are also available in 6 volt, 4 volt and even 2 volt, single cell blocks.

Batteries can be connected in series to achieve whatever voltage is required (add the number of 2 volt cells) and in parallel to achieve the capacity required (add the capacities of each parallel battery or string of batteries) . For larger systems, a number of series connected strings maybe connected in parallel with each other. This achieves both a higher voltage and capacity.

Two ConceptsThree basic applications
  1. Sealed or Regulated Lead Acid VRAL

  2. Open-Vented

  1. Sealed or Regulated Lead Acid VRAL

  2. Automotive (starter i.e. Cars, commercial vehicles)

  3. Open-Vented

VRLA has in many instances replaced the open-vented type.

The Lead-acid Battery

There are two concepts in lead-acid batteries and three basic applications.

Two ConceptsThree basic applications
  1. Sealed or Regulated Lead Acid VRAL

  2. Open-Vented

  1. Sealed or Regulated Lead Acid VRAL

  2. Automotive (starter i.e. Cars, commercial vehicles)

  3. Open-Vented

VRLA has in many instances replaced the open-vented type.

         This guide is focused on Industrial Standby applications and NOT Automotive or Traction use.

Industrial Batteries
         Industrial batteries are available from two distinct groups with the following features.

         Note: VRLA have superseded open-vented in many applications

•Older technology
•Require separated battery room
•Regular routine maintenance
•Separate safety requirements
•Store/use in vertical position
•Can require extensive cabling
•Environmentally friendly
•Use directly in office environment
•Low maintenance-”maintenance free”
•Self-contained. Safe
•Store/use in any orientation
•Can be used internal or adjacent to load

Note: The term sealed lead-acid SLA is an old acronym Considered misleading and is now replaced by Valve Regulated Lead Acid VRLA.

Typical VRLA battery applications

Typical Applications

It is vitally important to define your priority before size of battery.

These include:
High rate performance/Long life-unattended/High cycle life/Cost effectiveness

Telecom Communication Utility UPS Marine Cable Television Alarm system Security Equipment

Medical Equipment Electronic Test Equipment

Portable Television & Video Equipment
Power Tools Solar Power Lighting
Toy Vehicles Wheelchair Golf Trolleys
Semi-traction Lawn Mowers Lifting Equipment

To optimize battery duty and life for your application, make sure you choose the right product from the BSB range.


How to choose the right size of battery

 As mentioned earlier, batteries come in all shapes and size, from types no larger than a shirt button, to a battery system filling an entire room.
 To find the size of battery you require you generally need two pieces of information, battery load and back-up times. (Note: other factors may also have an effect).

Battery Load

 Whether you power lights, motors, electronic equipment or a toy vehicle you equipment will draw a load in AMPS. If this is unknown then the equipment will have a rating expressed in Watts which may simply be converted to Amps by dividing the value by the normal voltage of the system.

Back-up Time

 This is the time you require the battery to support the load described above and is often called Autonomy or discharge time.

 Example: To power a cordless electric tool for a total of 3.0 hours before recharging. With these two pieces of information use our selection graph to plot an intersection point from which you will determine a required size or capacity in Amp. hours (Ah).

Our figure has been rationalized into rounded figures of capacity. If your intersection point falls between two lines choose the next highest value.

Always choose a suitable sized battery from the ranges appropriate to your application.

You may notice that the chosen capacity in Amp hours is often higher than the Value of Amps x Hours used, in our example using 10AMPS x 3 HRS = 30Ah and the chosen option being 38 Ah. This is because the capacity of each NP battery is stated at the 20 hour discharge rate. You will only get full capacity if discharged over that length of time.


Correct charging of a VRLA battery is essential in optimizing battery performance and life. Although a constant voltage charge should be applied, optimum charging also depends on temperature (Nominally 20 degree), charge current (max 1/4 battery capacity) and ripple current (minimum) . Two basic categories of charging exist.

To find the size of battery you require you generally need two pieces of information, battery load and back-up times. (Note: other factors may also have an effect).

 This charging method is used in applications such as emergency back-up when the battery is required only upon mains failure e.g., continuously on charge and consequently the recommended voltages are slightly lower than cyclic charging so as not to damage the battery.

 Cyclic charging is used in applications where the battery is repeatedly discharged then charged, e.g. Portable equipment, Wheel Chairs, Golf trolleys etc.
 A higher charging voltage is used but should NEVER be left on indefinitely since is will overcharge and destroy the battery.

Note: For optimum performance always recharge a battery immediately after discharging. Consult the individual battery specification for the correct charging voltage or contact BSB Technical Department


The Storage or shelf life of a VRLA battery is usually between 12 and 18 months at 20 degree starting From a charged condition.
 Warning :
 Never store in a discharged or partially discharged state.
 Always store in a dry, clean, cool environment in a fully packaged condition.
 If storage of 12 months or longer is required supplementary charging will be require

Battery Care
 Each BSB VRLA battery is supplied I a charged condition having passed stringent quality checks.To ensure optimum battery performance and life, it helps to take care of your battery by observing the following:

 Warning – Never leave a VRLA Battery in a discharged state.
 If a battery has an open-circuit voltage lower than its rated value, then sulphation may well be the cause.
 When a battery is left a discharged state or for prolonged periods of storage, lead sulphate crystals begin to form acting as a barrier to recharge and will prevent normal battery operation.
 Depending on the degree of sulphation, battery may be recovered from this condition by constant current charging at a higher voltage with the current limited to one tenth of the battery capacity for a maximum of 12 hours.

Note: The applied voltage will exceed the normal recommendation and so the battery must be monitored (not left unattended) and removed from charge if excess heat is dissipated. The voltage required to «force» this maximum current into the battery will reduce as the battery recovers until normal charging can take place.

In extreme circumstances a battery may never fully recover from sulphation and must therefore be replaced.

 As mentioned in Section 4 optimum charging relies mainly on voltage, current and temperature factors which are interrelated and all of which can cause overcharge.
 Excessive charge voltages will force a high overcharge current into the battery, which will dissipate as heat, and may cause gas emission through the safety valve. Within a short period of time this will corrode the positive plate material and accelerate the battery towards end-of-life.

Under these conditions the heat produced inside the battery can lead to thermal runaway due to the increased electrochemical reaction within the battery. The battery may swell before failing and will be irrecoverable from this state. This situation is potentially dangerous.

 Warning – Heat Kills Batteries.
 The recommended normal operating temperature is 20°C.
 HIGH TEMPERATURE will reduce battery service life often quite dramatically. In extreme cases this can cause Thermal Runaway, resulting in high oxygen/hydrogen gas production and battery swelling. Batteries are irrecoverable from this condition and should be replaced.