VRLA stands for valve regulated lead-acid and is the designation for low maintenancelead-acid batteries, also called recombinant batteries. VRLA batteries are commonly further classified as:

1 Absorbent glass mat battery

2Gel battery

Vrla batterieshave a pressure relief valve which will activate when the battery is recharged at high voltage (typically greater than 2.30 volts per cell, a 12 volt battery has 6 cells). Valve activation allows some of the active material to escape thus decreasing the overall capacity of the battery. The lids (covers) typically have gas diffusers built into them that allow safe dispersal of any excess hydrogen that may be formed during overcharge. They are not permanently sealed, but are maintenance free; and they can be oriented in any manner, unlike normal lead-acid batteries which must be kept upright to avoid acid spills and to keep the plates' orientation vertical.

At high currents, electrolysis of water occurs, expelling hydrogen and oxygen gas through the battery's valves. Care must be taken to prevent short circuits and rapid charging. Charging with a constant voltage (called the float charge voltage; 2.26 V per cell for a lead-acid chemistry) can cause a rapid initial current, so therefore it is suggested to begin with a constant current, using constant voltage only for the final portion of the charging. However, the float charge voltage should not be exceeded by much for typical usage, so the switch between the two modes typically occurs when the float voltage is needed to sustain the charging current through the battery's internal resistance (as per Ohm's Law). The easiest way to implement this is to use a constant voltage device with a current limiter