Why the actual capacity of a battery during discharge seems lower?
Introduction
Batteries have become an integral part of our daily lives, powering everything from our smartphones to electric cars. However, have you ever wondered why the actual capacity of a battery during discharge falls short of its rated capacity? This article explores the reasons behind this phenomenon and why it is important to understand the limitations of batteries.
Capacity Rating of Batteries
Capacity rating of batteries is an important parameter that helps us understand the amount of energy that can be stored in the battery and how long it can power a device. The capacity rating of a battery is generally expressed in ampere-hours (Ah) or milliampere-hours (mAh) and is based on the theoretical capacity of the battery. The theoretical capacity is the maximum amount of energy that can be stored in the battery if it could be completely charged and discharged under ideal conditions.
Actual Capacity of Batteries
The actual capacity of batteries during discharge is always lower than the rated capacity. This is because batteries suffer from a variety of losses during their discharge cycle, including:
Internal Resistance Losses
All batteries have internal resistance due to their chemical composition and construction. This resistance causes energy to be lost as heat as the battery is discharged. The higher the resistance, the greater the energy loss and the lower the actual capacity of the battery.
Chemical Losses
During discharge, chemical reactions occur within the battery that can result in the loss of energy. For example, in lead-acid batteries, the sulfuric acid in the electrolyte can react with the lead plates to form lead sulfate, which reduces the capacity of the battery.
Temperature Losses
The actual capacity of a battery is also affected by temperature. As the temperature of the battery increases, the resistance of the battery decreases, causing more current to flow. This results in a higher rate of discharge, but it also increases the losses due to internal resistance and chemical reactions.
Cutoff Voltage
The rated capacity of a battery is based on a specific cutoff voltage. As the battery discharges, the voltage drops, and when it reaches the cutoff voltage, the battery is considered to be fully discharged. However, the actual capacity of the battery may be less than the rated capacity if the device using the battery has a lower cutoff voltage.
Conclusion
The actual capacity of batteries during discharge is always lower than the rated capacity due to losses caused by internal resistance, chemical reactions, temperature, and cutoff voltage. Understanding the limitations of batteries is important when designing devices that use them to ensure they operate reliably and for the expected duration. It is also important to properly maintain batteries to minimize these losses and extend their useful life.
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