Battery Capacity

Battery Capacity is the measure of the total energy stored in the battery and it helps us to analyze the performance and efficiency of the batteries. As we know, a battery is defined as an arrangement of electrochemical cells that works as a power source when there is no power source available and is used widely in today’s world. From small electronic gadgets to large-scale power grids, batteries are used everywhere. Thus, understanding the Battery and its capacity became more essential to understand these appliances and use cases.

In this article, we have explained one such important topic related to battery technology i.e., Battery Capacity. We will learn about this topic as well as its formula and how to use this formula to calculate the battery capacities of various different systems. Other than that we will also learn how to derive this formula as well. So, let’s start learning about the very important concept of “Battery Capacity”.

Battery Capacity Definition

Battery Capacity is defined as the product of the electric current flowing in or out of the battery in amperes and the time duration expressed in hours.

Battery Capacity influences the time for which a device can operate without using power from any other sources. For example, a smartphone with higher battery capacity will last longer without charging compared to a device with less battery capacity, assuming all the other factors remain the same.

Unit of Battery Capacity

The unit commonly used to measure battery capacity is the ampere-hour (Ah) or its subunit i.e., milliampere-hour (mAh). Other than these two units higher capacity batteries are measured in watt hour or kilowatt hour.

Ampere-hour (Ah): This unit of battery capacity represents how much current battery can provide for 1 hour. For example, a battery with a capacity of 2 Ah, can provide a 2-ampere current for 1 hour before it needs charging again.

Similarly, we can define other units as well.

Battery Capacity Formula

The formula for calculating battery storage capacity is given below:

Battery Capacity = Current (in Amperes) × Time (in hours)

Where,

• Battery Capacity represents the total amount of electrical energy a battery can store, typically measured in ampere-hours (Ah) or watt-hours (Wh).
• Current denotes the electrical current flowing in or out of the battery, measured in amperes (A).
• Time refers to the duration for which the battery sustains a specific current, expressed in hours (h).

Derivation of Battery Capacity Formula

The formula for battery capacity can be derived from the fundamental relationship between electrical current and time. To determine the amount of charge (Q) transferred during a specific period, we employ the equation:

Q = I × t

Where,

• Q denotes the charge in coulombs (C),
• I denotes the current in amperes (A),
• t refers to the time in seconds (s).

To convert the charge to ampere-hours (Ah) as coulomb is Ampere second, we divide Q by 3,600, which corresponds to the number of seconds in an hour:

Q (in Ah) = Q (in C) / 3,600

Since battery capacity is defined as the charge it can store, we can equate it to Q (in Ah):

By substituting the formula for charge (Q), we obtain:

Battery Capacity (in Ah) = (I × t) / 3,600

Which is the required formula.

Factors Affecting Battery Capacity

There are various factors that affect the battery capacity such as the chemistry of the substances used in the making of the battery to external factors such as temperature. Let’s discuss these factors in detail as follows:

Battery Chemistry and Type

The chemistry of the substances from which the battery is constructed plays a major role in the efficiency and capacity of the battery. As chemical reactions are involved in the flow of electrons that are responsible for the current flowing from the battery to the associated circuit and at the time of charging the undesirable chemical processes that take place when a battery is charged and drained also decrease its capacity to store power.

Also, types of the battery also affect this by the same principle, as changing chemistry also changes the types of batteries such as Li-ion, Li-polymer, Na-Ion, etc.

Aging and Life Cycle

Consider a battery with a capacity of C to start with; Over time the capacity decreases due to

• Aging or Time: calendar life(typically 1% to 2% of capacity loss per year)
• Charge-discharge cycles: as batteries are charged/discharged, battery capacity decreases.

Temperature and Environmental conditions

We know that battery capacity is directly proportional to the temperature which means, battery capacity is reduced as the temperature goes down and increased as the temperature increases. Also, battery life reduces at higher temperatures even though battery capacity at higher temperatures is higher but it shortened battery life. battery capacity is reduced by 50% at -22 degrees F- but battery life is increased by about 60% for the same.

Applications of Battery

In the modern world, batteries are the most important commodities, from smartphone to cars to future electric grids all uses the battery as their major component. Some other applications of the batteries are as follows:

• Lead Acid Battery: Used in automobiles for starting and lighting purposes, electric vehicles, air traffic control, for light and fans in trains, etc.
• Nickel-Cadmium Battery: it is largely used in railways for lights and air conditioning systems, in emergency power supply, and also in military airplanes and helicopters.
• NiMH [Nickel Metal Hydride] Battery: It is widely used in cellular phones, portable computers and laptops, digital Cameras, and electronic toys.
• Lithium-Ion Battery: it is majorly used in calculators, medical devices, portable radios, electric razors, etc.
• SMF [Sealed Maintenance Free] Battery: it is used in telecommunication systems, fire alarms, security systems, etc.

Battery Energy Storage System

Battery energy storage systems are essentially rechargeable systems that can store energy from solar arrays or the electric grid and discharge this energy later during times of high demand beyond balancing the intermittency of renewable energy batteries offer multiple solutions as a fast stacking reserve they can inject energy whenever wherever there is a shortfall at the distribution level.

Tips for maximizing the battery capacity and lifespan:

To maximize the battery storage capacity and lifespan here are some tips that must be followed:

• Avoid extreme temperature: don’t put your battery in very low or very high temperatures as it affects the battery life always try to store and operate your battery in a moderate temperature.
• Never overcharge your battery: avoid overcharging your battery as it causes stress and can reduce the lifespan of your battery.
• Don’t leave your batteries unused: Avoid leaving your batteries unused for a long period of time as it can lead to deep discharge of your battery.
• Avoid fast charging: fast charging can lead to overheating which can damage the battery life, so try to avoid fast charging if not necessary.

Read More:

• Cells and Batteries
• Who invented Battery?
• Weirdest Battery

Solved Problems on Battery Capacity

Problem 1: If a Battery allows a current of 7 amperes to go through it for 8 hours, calculate its storage capacity in amp-hour (Ah).

Solution:

By using the formula:

Battery Capacity (in Ah) = (Current × Time)

⇒ Battery Capacity = (7 A × 8 h)

⇒ Battery Capacity =  56 Ah

Problem 2: A battery has a storage capacity of 70 ampere-hours (Ah) and gives a constant current of 4 amperes. How long will the battery last?

Solution:

Using the rearranged formula:

Time (in hours) = (Battery Capacity) / Current

⇒ Time = (70 Ah ) / 4 A

⇒ Time = 17.5 hours

Problem 3: There is a battery with a storage capacity of 60 watt-hours (Wh) and a constant current of 20 amperes with 1 volt. Find how long will the battery last.

Solution:

As we know, P = VI = 20 × 1 = 20 Watts

Thus,  Time (in hours) = Battery Capacity (in Wh) / Power (in watts)

⇒ Time = 60 Wh / 20 watts

⇒ Time = 3 hours

Problem 4: A battery has a storage capacity of 80 ampere-hours (Ah) allowing a current of 4 amperes for 6 hours. Calculate the total amount of charge transferred during the given time.

Solution:

Using the formula:

Charge (in coulombs) = Current × Time × 3,600

⇒ Charge = 4 A × 6 h × 3,600

⇒ Charge = 86,400 coulombs

Problem 5: A battery with a storage capacity of 100 ampere-hours (Ah) and it is discharged with a constant current of 10 amperes. How long will it take to fully discharge the battery?

Solution:

Using the rearranged formula:

Time (in hours) = Battery Capacity (in Ah) / Current

⇒ Time = 100 Ah / 10 A

⇒ Time = 10 hours

FAQs on Battery Capacity

Q1: Define Battery Capacity.

Answer:

Battery capacity refers to the product of the electric current flowing in or out of the battery in amperes and the time duration expressed in hours. .

Q2: What Factors affect Battery Capacity?

Answer:

There are various factors can impact battery capacity, including temperature, discharge rate, aging, and the specific chemistry of the battery.

Q3: Can Battery Capacity Degrade over Time?

Answer:

Yes, over time, battery capacity may go down as a result of things like usage, charging cycles, exposure to extreme temperatures, and ageing

Q4: Can Battery Capacity be Increased?

Answer:

No, Battery capacity is cannot directly increased as it is determined by the physical characteristics of the battery.

Q5: How is Battery Capacity Determined?

Answer:

Battery capacity is determined through the physical characteristics that how much electric current it can pass under specific conditions.