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What Is the Energy and Capacity of the Battery ? What Is the Relationship Between Them?

#1-What Is Battery Energy?

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The battery energy represents the maximum power that can be stored in the power battery of a vehicle. It is one of the important indicators to measure the performance of the battery. Said that his electric car is equipped with a “xx degree battery“.

The energy of the power battery is also measured in kilowatt-hours. For example, the Tesla Model 3 long-range version is equipped with a 77kWh battery pack. The physical meaning behind it is that if this battery is used to drive a 100kW motor, the energy it provides can theoretically keep the motor running for 0.77 hours.

#2-What Is the Battery Capacity?

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Battery capacity refers to the amount of power a battery can store. The unit of battery capacity is “mAh”. When measuring large-capacity batteries such as lead-acid batteries, for convenience, it is generally expressed in “Ah”, 1Ah=1000mAh. That is, a current of 1A is charged for one hour, which is 3600 coulombs. We often see a 4400mAh battery on devices such as mobile phones and power banks; it means that if the working current is 10mA, it can work continuously for 440 hours; power banks generally have specifications ranging from thousands to tens of thousands of mAh.
Another example is that the rated capacity of the battery is 1300mAh. If the battery is discharged with a current of 0.1C (C is the battery capacity) or 130mA, then the battery can continue to work for 10 hours (1300mAh/130mA=10h); if the discharge current is 1300mA, then The power supply time is only about 1 hour (the actual working time is due to the actual working time of the battery).
There are some differences due to individual differences in actual capacity).
This is an analysis in an ideal state. The actual current of a digital device cannot always be constant at a certain value (taking a digital camera as an example, the working current will be larger due to the opening or closing of LCD display, flash and other components. change), so the time the battery can power a device can only be an approximate value, and this value can only be estimated through actual operating experience.

#3-What Is the Relationship Between Battery Energy and Capacity?

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Simply put, the battery capacity multiplied by the nominal voltage is energy.
For example: your battery capacity is 2000mAh, and the nominal voltage of the general battery is calculated according to 3.7V, then your power is 2000mAh*3.7V=7.4wh=0.0074kwh.

Usually, the mobile phones we use often have only one battery cell, so it is possible to use the capacity to express the performance of the battery; and the power battery pack of a new energy vehicle has many batteries, so it is more convenient to use energy to express the performance. Intuitive.

For a cell, its capacity and voltage platform (rated voltage) are determined by its own material properties, and the capacity multiplied by the voltage is the energy of the cell.
That is: Kwh = 1000 * Ah * V, 1Kwh is what we often call one kilowatt-hour of electricity.
The capacity determines the maximum value of your charge and discharge current. For example, the maximum charge current of a 50Ah capacity is 75A, and the maximum discharge current is 150A. Of course, this depends on the cell material.

Energy determines how far your electric car can run, such as 50kwh energy, generally can travel 250kw-400kw.

For disposable alkaline or carbon dry batteries, generally neither energy nor capacity is mentioned. According to the provisions of IEC60086, only duration is specified. For disposable batteries, they cannot be charged, and once the electric energy is consumed, it cannot be restored. . There will be a capacity value in the process of discharge, but this value is not fixed, it is the capacity value obtained under certain discharge conditions. Such as alkaline AA batteries, capacity: 2400mAh(under 10ohm, 1h/d discharge to 0.9V), and capacity: 2800mAh(under 25mA, 24h/d discharge to 0.8V)

For more knowledge about energy, capacity, power, voltage, current, please follow my blog

Carl Zhang

Carl Zhang

I am a senior sales with 15 years in the battery industry and a bachelor's degree in economics.
I will be sharing some of my expertise on batteries and my insights into the battery industry in my blog, which should help you with your purchases in China.

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