What is a Lead Acid Battery?
The Lead Acid battery is a dependable and cost-effective battery type and it is widely used in automobiles, wheelchairs, scooters, golf cars, forklifts and as UPS batteries. This is due to their ability to provide high surge currents, which are useful for powering starter motors, and their low cost. Even though Lead Acid batteries are the oldest type of rechargeable battery, they are still widely popular nowadays.
A little history of Lead-based batteries and the birth of SLA
The lead acid was invented by Gaston Planté in 1859 and it became the first rechargeable battery used commercially. The prototype consisted of two lead sheets divided by strips made from rubber and rolled into a spiral. This design was later improved by Camille Faure and it became easier to mass-produce. In the 1970s the Sealed Lead Acid battery was developed. Its design prevented leakage and made it easier to transport and use in different positions.
The Sealed Lead Acid
To begin we need to clarify that the term “sealed” is loosely used here as no lead acid battery can be totally sealed. There is a valve to control the venting of gases during stressful charge and rapid discharge. In order to enable the battery to work in any orientation without leaking the battery designers looked at designs of nickel and lithium based systems. Instead of submerging the lead sheets in liquid they impregnated the electrolyte into a dampened separator. Possibly the most noteworthy advantage of the sealed lead acid is the ability to prevent water loss by creating water from oxygen and hydrogen. The SLA batteries also have less electrolyte than the flooded type and are sometimes referred as “acid-starved”. The SLA is often used in the healthcare sector and in retirement homes, due to its affordable price and low maintenance. It is also popular as power backup for banks, airports, cellular towers and others.
There are a few types of Sealed Lead Acid batteries. The most common are GEL batteries and AGM (Absorbent Glass Mat). The first type utilizes a sylica type gel that suspends the electrolyte in a paste. The AGM design suspends the electrolyte in special glass mat. This leads to faster charging and instant high load currents on demand. The AGM is typically used for starter batteries. The capacity of AGM fades gradually in contrast of that of GEL, which stays at high performance for longer time but at the end of its life it abruptly drops. Generally AGM is cheaper than Gel. Another advantage of the AGM is that it prevents the vertical motion of the electrolyte in the battery, thus preventing the heavier acid molecules from settling to the bottom and making the bottom plates wear out faster. This eliminates the need to try to mix the electrolytes and avoiding one of the most common reasons of ruined car batteries. Gel cells share a lot of the AGM characteristics and advantages. They are often less susceptible to evaporation and require very little maintenance. They also have lower freezing and higher boiling temperatures which make them suitable for more extreme conditions. The optimum temperature however is 25°C (77°F) and every substantial increase will lead to shorter battery life.
When overcharged SLA batteries gas and the vent valve is activated. Repeated venting can cause water depletion and dry-out. Consequently the batteries cannot be charged to their full potential and the limit of the voltage must be set lower.