A battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its negative terminal is the anode.The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term “battery” specifically referred to a device composed of multiple cells; however, the usage has evolved to include devices composed of a single cell.
Batteries come in many shapes and sizes, from miniature cells used to power hearing aids and wristwatches to, at the largest extreme, huge battery banks the size of rooms that provide standby or emergency power for telephone exchanges and computer data centers. Batteries have much lower specific energy (energy per unit mass) than common fuels such as gasoline. In automobiles, this is somewhat offset by the higher efficiency of electric motors in converting electrical energy to mechanical work, compared to combustion engines.
Rechargeable batteries (also known as secondary cells) are batteries that potentially consist of reversible cell reactions that allow them to recharge, or regain their cell potential, through the work done by passing currents of electricity.
A 12V 2.8Ah (ampere-hour) battery is a type of rechargeable battery that provides 12 volts of electrical potential and can deliver a current of 2.8 amperes for one hour. The “12V” indicates its voltage, and the “2.8Ah” specifies its capacity, which is a measure of how much energy the battery can store and deliver.
Here’s what these specifications mean:
Voltage (12V): The voltage of the battery is 12 volts. This is the electrical potential difference between the positive and negative terminals of the battery. Many devices and systems, such as car batteries, use 12-volt batteries.
Capacity (2.8Ah): The capacity of the battery is 2.8 ampere-hours. This means the battery can deliver a continuous current of 2.8 amperes for one hour before it’s completely discharged. Alternatively, it can deliver a lower current for a longer time. For example, if you draw 1.4 amperes from the battery, it should last for approximately 2 hours (2.8Ah / 1.4A = 2 hours).