In basic electrochemistry and circuit terminology, a battery is a device composed of one or more chemical cells that convert stored chemical energy into electrical energy—select the most accurate completion.

Introduction / Context:
Batteries power everything from wristwatches to electric vehicles. Despite the ubiquity of the term “battery,” learners often confuse it with other energy-conversion devices such as solar or piezoelectric elements. This item checks foundational vocabulary in electrical engineering and physics: what a battery is made of and how it produces electrical energy.

Given Data / Assumptions:

• The question asks about the correct constituent unit of a battery.
• No particular chemistry (lead-acid, Li-ion, NiMH) is assumed.
• We focus on conventional definitions used in textbooks and standards.

Concept / Approach:
A single electrochemical “cell” generates electrical energy by redox reactions at two electrodes separated by an electrolyte. A “battery” strictly means one cell or, more commonly, multiple cells connected together to raise voltage, capacity, or both. Therefore, the most precise statement is that a battery is composed of one or more chemical cells.

Step-by-Step Solution:
1) Identify the nature of a battery: an electrochemical device.2) Recognize the basic unit: the chemical cell, which provides an electromotive force via redox chemistry.3) Connect terminology: multiple cells in series increase voltage; in parallel they increase available current (capacity).4) Conclude the accurate completion: “chemical cells.”

Verification / Alternative check:
Open any cell-level spec sheet (e.g., a “18650 Li-ion cell”). Battery packs list configurations such as 3S2P indicating 3 cells in series and 2 in parallel, reaffirming that batteries are assemblies of chemical cells.

Why Other Options Are Wrong:

• Voltage generators: Vague; many devices generate voltage, not specifically what constitutes a battery.
• Solar cells: Photovoltaic devices convert light to electricity, not chemical energy.
• Piezoelectric cells: Convert mechanical strain to electricity; not a battery.
• None of the above: Incorrect because “chemical cells” is correct.

Common Pitfalls:
Using “battery” for any energy source can blur distinctions among electrochemical, photovoltaic, and electromechanical devices. Precision matters in design and troubleshooting.

Final Answer:
chemical cells.