CBSE Class 12-science Answered

In electronics, a battery is two or more electrochemical cells which store chemical energy and make it available as electrical energy. Common usage has evolved to include a single electrical cell in the definition. There are many types of electrochemical cells, including galvanic cells, electrolytic cells, fuel cells, flow cells and voltaic piles.One common division of batteries distinguishes two types: primary (disposable) and secondary (rechargeable). Primary batteries are designed to be used once only because they use up their chemicals in an effectively irreversible reaction. Secondary batteries can be recharged because the chemical reactions they use are reversible; they are recharged by running a charging current through the battery, but in an opposite direction to the discharge current.Secondary, also called rechargeable batteries can be charged and discharged many times before wearing out. After wearing out some batteries can be recycled 

For this reason, a battery capacity rating is always related to an expected discharge duration—the standard duration is 20 hours.

where

Q is the battery capacity (typically given in mA·h).

I is the current drawn from battery (mA).

t is the amount of time (in hours) that a battery can sustainThe relationship between current, discharge time, and capacity for a lead acid battery is expressed by Peukert's law. The efficiency of a battery is different at different discharge rates. When discharging at low rate, the battery's energy is delivered more efficiently than at higher discharge ratesThe National Aeronautics and Space Administration (NASA) recognized the crucial importance of batteries very early in the space program.^[55] has funded many programs to develop batteries for use in spacecraft. Such batteries must be sturdy, resistant to conditions of cold and heat, and able to withstand the sterilization (microbiology) procedures required for all equipment aboard a spacecraft. The Jet Propulsion Laboratory, in Pasadena, California. is one of NASA's main recipients of research and development funding. NASA's battery work has included studies on nickel-cadmium (Ni-Cad), nickel-hydrogen (NiH), nickel-metal-hydride (NiMH) and lithium batteries, among others