A primary battery is designed to deliver stored chemical energy through discharge rather than to recover that energy repeatedly by electrical charging. The distinction concerns the practical cell design and reaction reversibility, not whether a balanced chemical equation can be written in both directions.
During discharge, coupled oxidation and reduction at the electrodes supply an external electric current. Reaction products, morphology changes and parasitic processes determine how much active material remains accessible. A rechargeable battery instead manages those changes sufficiently well to recover useful capacity over repeated cycles; nominal chemical reversibility alone does not establish that capability.
New to topics? Read the docs here!