Sealed Lead-Acid Battery Buying Guide

Batteries are devices that convert stored chemical energy into electrical energy. Batteries are either intended for onetime or rechargeable use. They use a variety of different chemicals and metal components to develop and convert energy, such as zinc, carbon, alkaline, gels, and fiberglass. One of the major rechargeable battery types is the valve-regulated lead-acid (VRLA) battery, also known as the sealed lead-acid (SLA) battery. VRLAs are designed to maintain internal structural integrity, as the electrolyte is contained in a comparably spacious chamber. This space allows the electrolyte to quickly recharge for high energy yields over short periods of time.

Battery Basics

Classic battery construction involves an electrochemical storage device composed of a chargeable electrolyte contained in a chamber, which is connected to another cell into which ions are transferred. The points of connection are called terminals, and there is a positive terminal and a negative terminal on any battery. The transfer occurs due to electrochemical interaction between the negatively charged (anions) and positively charged (cation) ions. The ions undergo oxidation, during which they lose electrons, and the cations undergo reduction, during which they gain electrons. This ion transfer creates the charge that is stored and powers the battery. When the two terminals of the battery are connected by a wire, the electrochemical reaction begins to provide a charge. The wire can be attached to a load, which is an electrical device that requires the charge, such as a circuit or motor.

There are various methods of producing the electrochemical reaction within a battery shell. The VRLA uses a sealed lead container that features valves to vent built up pressure. The pressure is produced by the electrochemical reaction used to produce charge in the battery: hydrogen and oxygen combined in water. The valves self-regulate the pressure that develops during this reaction, allowing for a fast recharge period and minimalizing the amount of personal maintenance required. The cycle of charging and recharging the battery can dry out the battery cells, and these batteries must be rehydrated to maintain performance levels.

Variations in Sealed Lead-Acid Batteries

The types of variations available in sealed lead-acid battery design include cycle length and valve regulation.

Some SLA batteries are designed for starting motors, such as automotive engines. These starter SLA batteries must launch a high charge for a large initial current output in order to start the large engine. SLA starting batteries are designed to feature a large surface area connection for the engine load, often in the form of thin metal plates. The plates are connected to points on the engine so that when the battery is engaged, a strong current is quickly transferred to start the engine. SLA starting batteries are not designed to provide long-term electrical output, and extended use can cause corrosion and accelerated failure ratios.

Devices and vehicles that do require long-term current input can be powered by deep cycle SLA batteries. Deep cycle SLA batteries include plates similar to the starter variety, but the plates are much thicker and have a shorter diameter. The denser connection allows for a continuous charge to power the device or vehicle.

The sealed lead-acid batteries often have valves to regulate internal integrity. During charging processes, pressure can build up because of the combination of chemicals. Automatic valves release this pressure when sensors determine ventilation is needed. These valves are wholly automatic and prevent manual activation. In order to maintain a healthy level of ventilation with regards to pressure statistics, certain tests can be performed, such as resistance, conductance and impedance tests. These tests will measure capacity levels in the battery cell. Some VRLAs are designed to allow manual rehydration processes when these situations occur, lengthening battery life.