fuel cell

This term refers to a specific technology used in green energy and aerospace engineering. It is distinct from a battery because it does not store energy but rather generates it continuously as long as fuel and an oxidant are supplied. In technical discourse, it is often contrasted with internal combustion engines due to its higher efficiency and lack of direct carbon emissions at the point of use.

As a compound noun, it follows standard English countability rules. While the technology itself is a concept, the physical devices are discrete units that can be grouped into stacks to increase power output.