What do Ah, W, and Wh mean for lithium-ion batteries?

What do Ah, W, and Wh mean for lithium-ion batteries?

Ah, W, and Wh are common units for lithium-ion batteries, and sometimes they can be confused, making it difficult to distinguish the meanings of these three units.

1. The Meaning of Ah, W, and Wh

Ah (Ampere-hour)

This is the unit of battery capacity, used to indicate the ability of the battery to store electrical energy. 1Ah means that the battery can discharge for 1 hour at a current of 1 Ampere (A). Ah is the product of current (A) and time (h), so it measures how many hours of current the battery can provide under specific conditions.

W (Watt)

This is the unit of power, used to indicate the rate at which electrical energy is converted or used. 1W means converting or using 1 Joule (J) of energy per second. In the context of batteries, watts are often used to describe the discharge or charging rate of the battery.

Wh (Watt-hour)

This is the unit of energy, used to indicate the total energy stored by the battery. 1Wh means the battery can provide power at 1 Watt (W) for 1 hour. Wh is the product of power (W) and time (h), so it measures how many hours of power the battery can provide.

In summary, Ah is the unit for measuring battery capacity, Wh is the unit for measuring battery energy, and W is the unit for measuring power.

2. Conversion between Ah, W, and Wh

From Wh to Ah: Ah = Wh / V

From W to Wh: Wh = W × h

For batteries, voltage refers to the nominal voltage, with the unit V; the unit for time is h.

For example, if we know that a battery has a capacity of 10Ah and a voltage of 3.7V, we can calculate its energy (Wh) as follows:

Wh = 10Ah × 3.7V = 37Wh

3. Nominal Voltages of Various Lithium-ion Batteries

Nominal voltage refers to the average voltage of a battery or battery system under normal operating conditions. It is a basic parameter of the battery, indicating the designed voltage level of the battery.

Actual voltage will vary with the charging and discharging status of the battery. At full charge, the battery's voltage will be slightly higher than the nominal voltage, and at the end of discharge, the battery's voltage will be lower than the nominal voltage.