What is a Sealed Lead Acid Battery?

The sealed lead acid battery is by far one of the most popular batteries that we receive questions on here at High-Tech Battery. I have decided (finally) to post a few of the most common questions that I hear from customers regarding sealed lead acid batteries here in our Battery Information Center, so here it goes.


What exactly is a sealed lead acid battery?

A sealed lead acid battery is what is originally known as a VRLA battery, or a valve regulated lead acid battery. These batteries are a 100% rechargeable, and based off a lead acid design. These batteries are designed to be maintenance free (do not require the user to add water to the cells), and spill proof. These batteries can be mounted in any position and still operate to their full capacity without spilling a drop of acid.

You may be wondering where exactly the valve regulated part of the sealed lead acid battery comes into play. Every SLA (sealed lead acid) battery is designed with a special safety release valve. These valves act as a emergency pressure release system that activate to alleviate the build up of gases within the SLA battery. During a period of an extremely high rate of charge (extreme over-charging), gases will be generated inside the battery that could potentially build up to critical levels and force its way out - via exploding a side of the battery out, or a simple crack in one of the cell dividers. To prevent this from happening, all SLA batteries are designed with these small pressure release valves.


Are there different types of sealed lead acid batteries?

Yes, there are two different types of SLA batteries out on the market today - AGM, and GEL batteries.

AGM batteries utilize a special plating process which optimizes the effectiveness of electrolyte reaching the batteries lead plates. AGM stands for absorbed glass mat, which is essentially what the entire process consists of. A mat consisting of very thin glass fibers woven together is placed between the internal lead plates of the battery. This glass mat is capable of absorbing and holding the optimum amount of electrolyte between the plates for the lifetime of the battery. This technology cuts down on the use of electrolyte and increases the efficiency and power of the battery.

The infamous GEL battery (confused with AGM SLA batteries on a daily basis) utilize a special gel based mixture between the plates of the battery instead of the typical electrolyte found in the common flooded lead acid batteries (think car battery). In this case, the gel is a combination of silica fume and standard sulfuric acid to create a type of gelified electrolyte. This design enables the battery to suffer much less internal corrosion, thus increasing the overall life of the battery - assuming you take care of it properly

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The sealed lead acid battery is the most commonly used type of storage battery and is well-known for its various applications including UPS, automotive, medical devices and telecommunications. The battery is made up of cells, each cell consists of plates immersed in an electrolyte of dilute sulfuric acid. The construction of the lead acid battery is illustrated below.

Battery Terminals

Depending on the model, batteries come either with AMP Faston type terminals made of tin plated brass, post type terminals of the same composition with threaded nut and bolt hardware, or heavy duty flag terminals made of lead alloy. A special epoxy is used as sealing material surrounding the terminals.

Battery Plates (Electrodes)

Power Sonic utilizes the latest technology and equipment to cast grids from a lead-calcium alloy free of antimony. The small amount of calcium and tin in the grid alloy imparts strength to the plate and guarantees durability even in extensive cycle service. Lead dioxide paste is added to the grid to form the electrically active material. In the charged state, the negative plate paste is pure lead and that of the positive lead dioxide. Both of these are in a porous or spongy form to optimize surface area and thereby maximize capacity. The heavy duty lead calcium alloy grids provide an extra margin of performance and life in both cyclic and float applications and give unparalleled recovery from deep discharge.

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Electrolyte

Immobilized dilute sulphuric acid: H2S04.

Battery Relief Valve

In case of excessive gas pressure build-up inside the battery, the relief valve will open and relieve the pressure. The one-way valve not only ensures that no air gets into the battery where the oxygen would react with the plates causing internal discharge, but also represents an important safety device in the event of excessive overcharge. Vent release pressure is between 2-6 psi; the seal ring material is neoprene rubber.

Battery Separators

Power Sonic lead acid battery separators are made of non-woven glass fiber cloth with high heat and oxidation resistance. The material further offers superior electrolyte absorption and retaining ability, as well as excellent ion conductivity.

Battery Container & Case Sealing

Case and lid material is ABS, high impact, resin with high resistance to chemicals and flammability. Case and cover are made of non-conductive ABS plastic to UL94-HB like our PS- or UL94 V-0 like our PS- FR. Depending on the model the case sealing is ultrasonic, epoxy or heat seal.

For more information, please visit What is an AGM battery?.