Final answer:
Batteries go dead owing to the consumption and eventual depletion of their internal reactants, whereas fuel cells continue to operate as long as reactants are supplied because they are not limited by an internal supply.
Step-by-step explanation:
The reason batteries go dead, but fuel cells do not, is primarily because batteries undergo irreversible chemical reactions.
In a battery, there is a limited supply of reactants which are consumed to generate electricity, and as the reaction byproducts accumulate, they can interfere with the reaction, leading to the depletion of the battery's charge. In contrast, a fuel cell operates differently.
It requires a constant external supply of reactants and removal of products, allowing it to continuously generate electricity as long as the reactants are provided.
Therefore, fuel cells do not 'go dead' in the same way batteries do because their operation is based on a continuous flow of materials rather than a finite quantity contained within the device itself.