BATTERY Intoduction An electrical battery is one or more electrochemical cells that convert stored chemical energyinto electrical energy. Since the invention of the first battery (or "voltaic pile") in 1800 by AlessandroVolta, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales each year, with 6% annual growth.

TYPES OF BATTERY There are two types :  Primary batteries (disposable batteries),  Secondary batteries (rechargeable batteries)

PRIMARY BATTERY Primary batteries can produce current immediately on assembly. Disposable batteries are intended to be used once and discarded. These are most commonly used in portable devices that have low current drain, are only used intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available. Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against attempting to recharge primary cells.

SECONDARY BATTERY Secondary batteries must be charged before use; they are usually assembled with active materials in the discharged state. Rechargeable batteries or secondary cells can be recharged by applying electric current, which reverses the chemical reactions that occur during its use. Devices to supply the appropriate current are called chargers or rechargers.

Float working of batteries

VRLA BATTERY Introduction A VRLA battery (valve-regulated lead-acid battery) is the designation for low-maintenance lead-acid rechargeable batteries. Because of their construction, VRLA batteries do not require regular addition of water to the cells.VRLA batteries are commonly further classified as: Absorbed glass mat (AGM) battery Gel battery (gel cell) These batteries are often colloquially called sealed lead-acid batteries, but they always include a safety pressure relief valve.

Construction of VRLA Battery Fig. Power Stack Cell – Cut Section

The oxygen recombination principle: Reaction at positive plate : H 2 O = ½ O 2 + 2e– … (1) Reaction at negative plate : Pb + ½ O 2 =PbO… (2) PbO+H 2 SO 4 =PbSO 4 + H 2 O… (3) PbSO 4 + 2H+ + 2e–=Pb + H 2 SO 4 … (4) The total reaction at negative plate ½O 2 +2H+=H 2 O

CHARACTERSTICS OF “VRLA” BATTERY Maintenance free, valve-regulated lead-acid (VRLA) batteries ensure a reliable, effective and user friendly source of power. It is spill proof, leak proof and explosion resistant and there is no need to add water or to clean terminals. It has low self-discharge rate which eliminates the need for equalizing charges. The chemically inert glass ensures life long service. Gas evolution under float conditions is negligible. The water loss throughout life due to gassing is roughly 0.1% of the total electrolyte present in the cell. This will in no way affect performance and also eliminate the need for specially ventilated battery room and acid resisting flooring.

As the batteries can be installed in stacks, there will be considerable space saving also. Various capacities of Batteries are 120 AH, 200 AH, 400 AH, 600 AH, 1000 AH, 1500 AH, 2000 AH, 2500 AH, 3000 AH, 4000 AH and 5000 AH.

ADVANTAGE Purer lead in the plates, as each plate no longer needs to support its own weight, due to the sandwich construction with AGM matting. Traditional cells must support their own weight in the bath of acid. Fluid retention - un-spillable High specific power or power density, holding roughly 1.5x the AH capacity of flooded batteries due to purer lead Low internal resistance allowing them to be charged and discharged quite rapidly Depth of discharge for optimal performance is up to 80% while flooded batteries can only be rated up to 50% depth of discharge Water conservation - never requires addition of water Acid encapsulation in the matting Operation well below 0°F or -18 °C. Availability of UL, DOT, CE, Coast Guard, and Mil-Spec approved types Vibration resistance due to the sandwich construction.

DISADVANTAGE Cost. AGM automobile batteries for example, are typically about twice the price of flooded-cell batteries in a given BCI size group. AGM batteries have up to a 10 year lifespan. AGM batteries do not tolerate overcharging. Overcharging dissociates the water in the electrolyte, which is unable to be replaced, leading to premature failure