VRLA Battery Failure Modes

About 60% of VRLA batteries fail due to grid corrosion. As explained in our article titled: Lead Acid Battery Basics, battery charging, including float charging, is associated with water electrolysis which decomposes water into Hydrogen and Oxygen created at the positive plate. The valves in VRLA battery do not enable gasses venting into air, and most are recombined by a diffusion process to form water again. Still, corrosion due to oxidation of the grid on positive plates is unavoidable. The corrosion gradually reduces the amount of active material causing eventually total battery failure.

The corrosion process depends on the ratio of plate's surface area to weight. A thin, plate has larger surface area to grid weight, compared to thick plates containing a few thin wires. Hence,

thin grid has faster rate of corrosion per AH capacity. Therefore, UPS batteries, for short back up times, which need large area to provide the high currents, have low 3 to 5 years longevity. Whereas, UPS systems for longer back up times, such as used also in communication, use VRLA batteries with less plates but thick grids; which have higher lifetime, of up to 15 years.

Battery dry out, a term used to describe battery failure due to loss of electrolyte is the second main reason for battery malfunction, comprising more than 30% of battery failures. Presence of active material in the required quantity is mandatory to maintain battery capacity. Therefore Loss of electrolyte affects dramatically Battery's ability to continue providing power.

Overcharging is the main reason causing dry out failure. Normally recombination of Oxygen and Hydrogen gasses, replenishes almost full amount of water extracted from the acid by electrolysis reaction. However, even a small charging or float over voltage, above the correct voltage setting, or high rate of charging current, can produce oxygen and hydrogen at a higher rate compared to   the rate of recombination reaction. Thus, increasing the gas pressure in the battery, until the pressure relief valves open.

In VRLA batteries the electrolyte lost in the air through the valves due to overcharge, cannot be replaced, resulting in reduced battery capacity. Certain additional reactions, such as corrosion, contribute also to battery dry out by converting electrolyte in the battery to non active constituents.

As indicated above, 90 % of battery failures affecting battery longevity are caused by grid corrosion and battery dry out. Additional reasons, generally responsible to about 10% of total battery failures, most also caused due to grid corrosion or dry out, comprise of: cell shorting, cell opening, leakage, undercharge, poor internal or external interconnections, cell reversal and

thermal runaway.

If you want to know more about VRLA battery, you can just visit Leoch International, which is an excellent manufacturer of lead acid batteries. The company is a public company which has over 10 year’s history and it is very reliable and dependable. If you are interested in the company, you can search for more information in the internet. The office website is http://www.leoch.com.