What are VRLA batteries?

Valve-regulated lead acid (VRLA) batteries are sealed batteries fitted with a safety valve that allows the gas produced by overcharging or a cell fault to escape.

VRLA batteries are highly leak-proof and can be used in any type of situation. They are completely maintenance-free. VRLA batteries are also known as sealed lead acid (SLA) batteries.

There are two types of VRLA batteries:

• AGM batteries
  AGM stands for absorbent glass mat. In this battery type, the electrolyte is absorbed by a fleece mat made of fine glass fibre which has a capillary effect. AGM batteries are the most common type of VRLA batteries and can also withstand high discharging currents for short periods.
• Gel batteries
  In these batteries, the electrolyte is in a gel made from silica. Gel batteries generally have a longer lifetime and a lower self-discharge rate. They are also better suited to cyclic loads. The disadvantage of these batteries is that they are more sensitive to mechanical loads (impacts, vibration) and do not respond well to high discharging currents.

In addition to the sealed VRLA batteries, there are also sealed lead acid batteries of the kind used for starting vehicles.