Do Rechargeable Fire Extinguishers Have to Be Replaced?

There are two types of fire extinguishers: rechargeable and disposable. As the name suggests, a disposable fire extinguisher is one which must be thrown away once it's empty. A rechargeable fire extinguisher, on the other hand, can be refilled with its agent (usually water, dry powder, CO2, AFFF foam, or a vapourising liquid) when it's empty. Many owners of rechargeable fire extinguishers get confused by the prospect of replacement: is it necessary, and if so, when?