If voltage is not used up in a circuit then why does battery go flat?

Batteries do not go flat because voltage is used up. Voltage is the difference in electrical potential between two points in a circuit, and it is a measure of the electrical pressure that causes current to flow. Current, on the other hand, is the flow of electric charge, and it is measured in amperes.

Batteries go flat because they lose their ability to store chemical energy. When a battery is connected to a circuit, chemical reactions take place inside the battery that convert the stored chemical energy into electrical energy. This electrical energy is then used to power the devices connected to the circuit.

Over time, the chemical reactions inside a battery will eventually use up all of the available chemical energy, and the battery will go flat. This process can be accelerated by a number of factors, such as high temperatures, high discharge rates, and short circuits.

So, while voltage is not used up in a circuit, it is the loss of chemical energy that causes batteries to go flat.