I thought of these two nouns recently when I had to refill a flashlight.

Problem:
One of these in everyday speech is often misidentified as the other in discussions related to electricity.

Explanation:
In electrical terms,

• a “battery” is an electrically connected combination of two or more “cells”;
• a “cell” is something that converts chemical energy into electrical energy, usually via an electrolyte and two substances with different conductivities.

A “cell” typically has an electromotive force of about 1.5 volts.

In contrast, a “battery” has an electromotive force that equals 1.5 volts times the number of cells in the battery.

For example, the PP3 battery, which is commonly called a “9-volt battery” and truly is a “battery”, has an electromotive force of 9 volts because it comprises six “cells” within its case.

As another example, if you put four “D” cells in a flashlight, you have a six-volt battery in the flashlight.

In other words, although many dictionaries indicate that one of the definitions of “battery” is “cell”,

• this refers to everyday speech,
• this is not the primary definition, and
• this is technically incorrect.

Solution:
When it comes to electricity, use “cell” for the “AA”, “AAA”, “C”, and “D” units that can be bought in stores, and use “battery” to refer to a connected set of these units or to refer to the 9-volt, “PP3” unit popularly used in smoke detectors, alarm clocks, etc.