Battery energy is being “used up.”
Work Step by Step
Charges move through a circuit and return to the battery with less potential energy than they started with. The battery replenishes the potential energy of the charges, at the cost of its own chemical potential energy. When a battery is “dead” it is no longer able to supply potential energy. The question is ill-phrased, because if there is no battery energy, there is also no battery current or battery voltage or battery power. But if we have to pick one, it’s battery energy.