Article-Engineering

Valve regulated lead acid batteries

Main article: VRLA
The Valve Regulated Lead Acid (VRLA) battery is one of many types of lead-acid batteries. In a VRLA battery the hydrogen and oxygen produced in the cells largely recombine back into water. In this way there is minimal leakage, though some electrolyte still escapes if the recombination cannot keep up with gas evolution. Since VRLA batteries do not require (and make impossible) regular checking of the electrolyte level, they have been called Maintenance Free (MF) batteries. However, this is somewhat of a misnomer. VRLA cells do require maintenance. As electrolyte is lost, VRLA cells may experience "dry-out" and lose capacity. This can be detected by taking regular internal resistance, conductance or impedance measurements of cells. This type of testing should be conducted on a regular basis, as an indicator that more involved testing and maintenance may be required. Recent maintenance procedures have been developed allowing "rehydration" of cells that have experienced dry-out, often restoring significant amounts of the lost capacity.

VRLA types became popular on motorcycles because the acid electrolyte is absorbed into the medium which separates the plates, so it cannot spill. This medium also lends support to the plates which helps them better to withstand vibration. They are also popular in stationary applications such as telecommunications sites, due to their small footprint and flexibility of installation.

The electrical characteristics of VRLA batteries differ somewhat from wet-cell lead-acid batteries, and caution should be exercised in charging and discharging them.

Of the several types of VRLA batteries are the absorbent glass mat battery, gel battery, and sealed lead-acid battery.

Source: http://www.answers.com/topic/lead-acid-battery-1