There are two distinct types of lead acid batteries manufactured: Vented lead acid batteries (flooded), Valve regulated lead acid (VRLA) batteries. VRLA batteries offer a lot of advantages over other types of batteries.

VENTED LEAD ACID BATTERIES(FLOODED)

Vented lead acid batteries are commonly called “flooded”, “spillable” or “wet cell” batteries because of their conspicuous use of liquid electrolyte.

Lead acid batteries are the most often used to power vehicles and other motorized equipment. Lead acid batteries with a conventional charger are the predominant technology option, due to their low cost, reliability and well-established supply chain. The battery most common to everyone is the engine starting battery. The starter battery is designed to crank an engine with a momentary high-power load lasting a second or so. These batteries are most commonly 12 volt but can be found in 6 volt in older equipment and 24 volt in aircraft starting applications. These batteries are of different shapes and sizes but the rule of thumb is, the bigger the battery, the more power it will deliver. The other type of lead acid batteries found within motorized equipment is known as deep cycle and/or traction batteries. Marine applications, golf carts, fork lift trucks, ice resurfacers and other electric vehicles use deep cycle batteries which are designed to be completely discharged before recharging.

Thicker and stronger or solid plate grids are used for deep cycling applications. because charging causes excessive heat which can warp the plates. Thicker plates increase the longevity and cycle life of deep-cycle batteries as each time the battery is discharged and recharged, a small amount of active material is shed from the plates. A starter battery cannot be swapped with a deep-cycle battery or vice versa.

VALVE REGULATED LEAD ACID (VRLA) BATTERIES

Valve regulated lead acid (VRLA) batteries, also known as “sealed lead acid (SLA)”, “gel cell”, or “maintenance free” batteries, are low maintenance rechargeable sealed lead acid batteries. They limit inflow and outflow of gas to the cell, thus the term “valve regulated”. VRLA batteries are the most widely used battery type because of their high power density and ease of use. These batteries come in all shapes, voltages, amperages and sizes. VRLA batteries are considered to be “sealed” because they normally do not allow for the addition or loss of liquid. The term VRLA derives from the use of safety valves that allow pressure to be released when a fault condition causes internal gas to build up faster than it can be recombined.They are widely used as UPS backup batteries and deep cycle solar (renewable) energy storage batteries.

There are two primary types of VRLA batteries:

· Absorbed Glass Mat (AGM): AGM batteries differ from flooded lead acid batteries in that the electrolyte is held in the glass mats, as opposed to freely flooding the plates. The fibers that compose the fine glass mat do not absorb nor are they affected by the acidic electrolyte.

· Gel: gel cells add silica dust to the electrolyte, forming a thick putty-like gel. These are sometimes referred to as "silicone batteries". Unlike a flooded lead-acid battery, these batteries do not need to be kept upright. Gel batteries reduce the electrolyte evaporation, spillage (and subsequent corrosion problems) common to the wet-cell battery and boast greater resistance to shock and vibration.

VRLA batteries offer a lot of advantages over other types of batteries, such as:

· Maintenance-free

· Moderate life

· High rate capacity

· High charge efficiency

· No “memory effect” as observed with nickel-cadmium (NiCad) or nickel-metal hydride (NiMH) rechargeable batteries that causes them to hold less charge

· State of charge can be determined by measuring voltage

· Relatively low cost  

· Available in a variety of sizes and voltages