Batteries

A battery is an electrochemical device that stores energy and can provide power to electric circuits. Energy is stored by chemical means, with the chemistry used typically defining the type of battery. The earliest batteries were known as voltaic piles, and operated under the same principles as they work today. Batteries have two electrodes (an anode and a cathode) of a dissimilar material separated by an electrolyte, a medium by which ions can flow between the electrodes. The chemistry of the battery specifies whether the battery can be recharged (rechargeable) or if it is a primary type and is single use only. Rechargeable batteries have a reversible chemical reaction on their electrodes, whereas primary batteries do not.
Most common types of non-rechargeable batteries are of zinc-carbon or alkaline chemistry. Zinc-carbon batteries are a dry cell where the electrolyte is a paste rather than a liquid. Heavy-duty versions of these batteries can be based upon a zinc-chloride paste, as opposed to ammonium chloride. Alkaline batteries are available in both primary and rechargeable (secondary) types. Primary alkaline batteries use a chemistry based upon zinc and magnesium dioxide.
Rechargeable alkaline batteries are based upon similar chemistry to their primary counterparts. They are tweaked to optimize for recharging rather than capacity/energy density and are typically only about two-thirds the capacity. Lead-acid batteries are rechargeable, and typically used in high drain, high surge current applications. Vehicle batteries are typically lead-acid due to the high current drain load placed on it by the starter motor, which can be in the hundreds of amps. Valve Regulated Lead-Acid (VRLA) is a lower leakage (self-discharge) version of the lead acid. Gell and absorbed glass mat (AGM) batteries are other lead acid variants optimized for deep-cycle (high drain) applications.
Lithium-ion batteries are a type of high energy density rechargeable battery used in many applications, especially portable applications today. They are also used in high drain applications like electric vehicles. They are used because their chemistry has special characteristics that allow for very light, energy dense batteries with a high number of recharge cycles (caused by irreversible chemical changes in batteries) and little or no memory effect. Memory effect is a collection of effects where over time and discharge cycles, the effective capacity of the battery seems to reduce. This can be caused by temporary and permanent changes. NiCad (nickel-cadmium) and NMiH (nickel-metal hydride) are alternative chemistry rechargeable batteries. All rechargeable batteries have special voltage and current charging requirements over the charging process, referred to as a charging cycle.