The word "battery" doesn't have much of anything to do with stored energy. It derives from Latin battuere (to strike), via French, and originally meant wrought/forged metal articles. It came to mean a set of artillery pieces operating as a unit (a battery of guns), and then more broadly a set of various things that operate together and often are similar or identical to each other.
You can have a battery of tests to form a medical diagnosis: a set of tests, working together. You can also have an electrical battery, a set of cells working together for greater voltage or current than a single cell provides. A hydroelectric dam, a pressure vessel, or many other things that store energy are not batteries. (A single AA cell is also not a battery, technically speaking, but two or more of them together can form a battery.)
