How is the capacity of a battery measured?

The capacity of a battery is measured in milliampere-hours (mAh) or ampere-hours (Ah), indicating the amount of charge it can deliver.

The capacity of a battery is a measure of the amount of electric charge it can deliver at a specific voltage. Most commonly, this is measured in milliampere-hours (mAh) or ampere-hours (Ah). This unit essentially tells you how much current a battery can provide for a certain period. For instance, a battery rated at 1000 mAh can deliver a 1000mA (1A) current for one hour, or a 500mA current for two hours, or a 2000mA current for half an hour, and so on.

The capacity of a battery is determined by the chemical composition and physical size of the battery. Different types of batteries, such as alkaline, lithium-ion, or nickel-cadmium, have different energy densities, which means they can store different amounts of energy per unit volume or weight. The larger the battery, the more material there is to undergo the chemical reactions that produce electric charge, and therefore the higher the capacity.

However, it's important to note that the actual amount of energy a battery can deliver can be influenced by several factors. These include the rate at which the current is drawn (discharge rate), the required voltage, and the temperature. For example, drawing current at a higher rate can cause the battery's capacity to decrease due to internal resistance. Similarly, operating a battery at a lower temperature can also reduce its capacity because the chemical reactions that produce electricity are less efficient at lower temperatures.

In addition, the capacity of a battery can decrease over time due to repeated charge and discharge cycles. This is known as the battery's cycle life. Each time a battery goes through a charge-discharge cycle, its capacity is slightly reduced. This is why rechargeable batteries eventually need to be replaced.

In summary, the capacity of a battery is a measure of the amount of electric charge it can deliver, typically expressed in milliampere-hours or ampere-hours. It is determined by the battery's chemical composition and size, and can be influenced by factors such as discharge rate, operating conditions, and the number of charge-discharge cycles.