How Do SLA Batteries Actually Work?

We’ve learned a lot about SLA batteries through these tutorials and guides, but some may also be interested in how SLA batteries actually work. While it can be quite technical, it can offer an interesting insight into the world of batteries in general.

We’ve been taken through the history of batteries and the types of batteries out there, our main interest is understanding the Lead Acid battery which we have come to appreciate for its reliability and its price, you get a whole lot of bang for your buck.

Typically, the internal plates are made from lead alloy which is where the lead name comes in but there are usually a few other metals thrown in for added strength including antimony, calcium, tin and selenium. This added strength does come at a small price though as these metals can increase oxidization and each discharge/charge cycle permanently costs the battery a small amount of capacity. This is the case with most batteries but can be more significant with lead acid. Lead Acid batteries became Sealed Lead Acid batteries around the early 70’s, significantly reducing the need for maintenance.

While charging a sealed lead acid (SLA) battery can be a little on the slower side, its ability to operate in a range of temperatures and conditions, really does make it a versatile option for many vehicles and systems. 

Perhaps the most significant advantage of sealed lead acid is the ability to combine oxygen and hydrogen to create water and prevent dry out during cycling. The recombination occurs at a moderate pressure of 0.14 bar (2psi). The valve serves as a safety vent if the gas buildup rises. Repeated venting should be avoided as this will lead to an eventual dry-out.

The sealed lead acid battery is designed with a low over-voltage potential, prohibiting the battery from reaching its gas-generating potential during charge. Excess charging causes gassing, venting and subsequent water depletion and again, potential dry-out. 

We previously explored the main types of SLA batteries which includes starter, deep cycle and dual purpose (which is a combination of starter and deep cycle). The starter battery is designed to push out large currents quickly which is done through increasing the internal plates. These plates are thin and increase the surface area which allows for increased discharge. Conversely, deep cycle SLA batteries have fewer plates but with increased thickness allowing for a higher cycle count which gives it the ability to last a longer time.

Lead acid batteries are a complex system where electricity is produced by a chemical reaction between the material on the plates and the electrolyte. It’s this system that brings significant advantages to users of SLA batteries including price, durability, and reliability. It also has a decent shelf life, a wide range of operating temperatures and is relatively maintenance free. It is these advantages that make the SLA Battery a valuable asset for a variety of vehicles and devices including many important to homes and businesses alike.