The charged particles are always there - what runs down?

What gets used up?

When a battery is first connected to a bulb, the bulb warms up and lights up the surroundings. It is clear that something must be getting used up somewhere. According to the electric circuit model introduced, it should also be clear that it is the energy provided by the battery, which is gradually dissipated, as a result of the lighting and heating.

When all of the chemicals in the battery have reacted and the battery cannot supply any more energy, we say that the battery has gone flat. The charged particles stop moving and the bulb goes out. On first coming across these ideas, it is quite common for people to think that the electric current gets used up. However the current is simply the flow of charge that shifts energy. The charge is neither lost nor used up, so the current is the same everywhere in the electrical loop. What happens is that the store of energy in the battery empties as energy is dissipated through heating and lighting in the bulb.