Power in a Small Package
Batteries are everywhere: in phones, remote controls, cars, and countless other devices. They let us carry power with us, free from wall sockets and cables. We talk about a battery being charged or storing energy. But electricity itself is hard to store directly. So when a battery is full, what is really being held inside it, and how does it turn back into the power that runs our devices?
Energy Stored as Chemicals
The key idea is that a battery does not store electricity directly. Instead, it stores energy in chemical form. A battery is filled with specific chemical materials, and the energy is locked inside the chemical structure of those materials. This is called chemical potential energy. A charged battery is essentially holding a chemical reaction in a ready, waiting state, poised to happen but not yet released.
Inside the Battery
A battery has two main terminals, often called the electrodes: one positive and one negative. Between them is a substance called the electrolyte. The materials are arranged so that a chemical reaction wants to take place, but it cannot fully proceed until the battery is connected into a circuit. Until that connection is made, the energy stays safely stored in the chemicals, which is why a battery can sit unused and still hold its charge.
Releasing the Energy
When you connect a battery to a device, you complete a circuit, and the waiting chemical reaction begins. As the chemicals react, the reaction pushes electrons to flow out of the battery, through the device, and back. This flow of electrons is electric current, the electricity that powers the device. In a rechargeable battery, supplying electrical energy from outside can drive the reaction backwards, restoring the chemicals to their original state and storing energy once again.
Source
This article was written using information from Wikipedia.