Laptop battery made up of cells. Usually, 6 or more than six cells combine in a series and form a shape of the battery.
Each battery combines and makes a big power source. This power is enough for running a laptop.
A battery life depends upon cells life and cell depends on the chemical base. Every cell is made up of chemicals. These chemicals complete a chemical reaction and produce a small amount of energy.
It’s just like a transformation of energy from chemical to electric. This reaction decay the characteristic of chemicals. If we don’t use the battery it decays slowly but decays.
So, every battery has a fixed life period. We can increase it by not using but never can stop to decay.