Nominal Voltage and Capacity of Lithium-ion Batteries

A cell is an Electro-chemical reaction which is housed in a mechanical structure. Usually, the commonly available cells you find, like alkaline cells are called by their mechanical structure - AA, AAA, D size batteries are found in most stores today. Sometimes, they are referred to by their nominal voltage, for example you go to the store and say that you're looking for a 9 Volt battery, the attendant knows exactly what you're talking about.

You would have noticed that I'm using the terms cell and battery interchangeably. This is technically incorrect, but still used in today's communication. The difference between the two is that a battery comprises of two or more cells.

Let's get back to the first experiment. Take a cell lying around in your house and pay attention to a few key parameters listed on the packaging of the cell. For example, pick a AA cell to see if the packaging says what the nominal voltage is, what about capacity in Ampere-hours? Duracell markets its AA cells as long lasting, is their capacity higher than the unbranded AA cells available, or is it just a marketing statement?

Here are some 9V cells, you can see how the nominal voltage and capacity varies with manufacturer and chemistry. Try to generate a similar table for cells you find around the house or in store to see the variance.

​Ref: Michael Blue Jay

Nominal voltage is the standard voltage by which a cell is referred to. The actual voltage of the cell will vary around its nominal value. For example, a 3.7V nominal cell tells you that the voltage of the cell will be between 2.8V to 4.2V.

Capacity of a cell is usually measured in Ah. This represents the amount of charge the cell can hold. So a 5Ah cell, when fully charged holds 5Ah of charge, when charged half way holds 2.5Ah of charge.

With this experiment, you were introduced to two important parameters of cells which is nominal voltage and capacity​, understanding both of which is essential to understanding battery technology.