A battery is a device that stores electricity in chemical form inside a closed-energy system.
Long before the invention of electrical generators and grids batteries proved to be the main source of electricity, and still continue to serve this purpose.
There are batteries in different shapes. Some are very small, like the ones used in wristwatches, or smart phones, and some are as big as those used in cars and trucks. At the extreme, there are huge battery banks that are the size of rooms.
All batteries have three parts- an anode (the negative side), a cathode (positive side) and an electrolyte, a liquid or gel that contains electrically charged particles called ions.
When connected to an external circuit, the ions interact with the other two, and a chemical reaction takes place inside the battery.
This reaction results in the generation of electric current. This is how batteries function and provide electric power to all appliances in our house including mobile, phones, laptops, flashlights etc.