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IB DP Physics Study Notes

5.3.3 Batteries

Batteries, intricate collections of cells designed to transform chemical energy into electrical energy, are foundational to the operation of countless devices that pepper our modern lives. Their configuration, be it in series or parallel, holds paramount significance.

The Essence of Cells in a Battery

Understanding batteries starts with grasping the basic concept of a cell. A cell is a standalone unit capable of producing an electric current by converting chemical energy.

The Principle of Chemical Energy Conversion

  • Chemical reactions within a cell release energy.
  • This energy pushes electrons from the negative terminal to the positive terminal, setting up a voltage.
  • When a device is connected, this voltage drives a current through it.

Combination of Cells

The strength and duration of a battery's power can be tailored by arranging cells in specific configurations.

Series Combinations

  • Configuration: Cells connected end-to-end (positive terminal to the negative terminal of the next).
  • Voltage: Total voltage = Sum of individual cell voltages. So, if each cell provides V volts, and there are 'n' cells in series, the total voltage is nV.
  • Capacity: Remains unchanged. A series configuration doesn't augment the total energy content; it merely increases the voltage at which it's delivered.

Parallel Combinations

  • Configuration: All positive terminals linked together, and all negative terminals linked likewise.
  • Voltage: Remains constant across the combination, mirroring that of a single cell.
  • Capacity: It's an aggregate of all cells. If each cell boasts a capacity C and 'n' cells are interconnected in parallel, the total capacity burgeons to nC.

Advantages & Applications of Cell Combinations

Benefits of Series Combinations

  • Higher Output Voltage: Vital for devices necessitating elevated operating voltages.
  • Compact Design: Facilitates the usage of several smaller cells rather than one gigantic cell to attain a specific voltage.

Benefits of Parallel Combinations

  • Augmented Capacity: Ideal for devices where longevity, rather than voltage, is pivotal.
  • Operational Redundancy: A defunct cell doesn't render the device powerless; others compensate.

Real-world Applications

1. Household Devices: Gadgets like toys, torches, and TV remotes often deploy series configurations to fulfil their voltage needs.

2. Electric Vehicles (EVs): The heart of an EV, its battery, is a labyrinth of cells in both series (to boost voltage) and parallel (to amplify capacity). This design ensures optimal performance and range.

3. Energy Storage in Renewables: The sporadic nature of solar or wind energy necessitates robust storage solutions. Here, vast arrays of cells in parallel provide extended energy reserves.

4. Uninterruptible Power Supplies (UPS): In realms where power continuity is sacrosanct, UPS systems step in. They seamlessly combine series and parallel configurations to guarantee both requisite voltage and lasting backup.

Factors Governing the Efficiency of Combined Cells


It's cardinal that cells within a battery share voltage and capacity traits. A medley of disparate cells can compromise the battery's performance or inflict damage.

Ageing and Performance Degradation:

As cells age, their efficiency dwindles. Pairing old cells with new ones might spell a premature depletion of the former, pulling down the battery's overall efficiency.

Heat Dynamics:

Especially with parallel configurations, heat can be a formidable adversary. Efficient heat dissipation mechanisms are imperative to avert potential hazards and ensure the battery's longevity.

Internal Resistance:

All cells exhibit some internal resistance, which can play spoilsport, leading to energy losses. It's especially pronounced in series configurations. Ensuring low internal resistance can significantly ramp up the battery's output.

Capacity Matching:

For parallel configurations, ensuring that all cells have closely matched capacities is crucial. A cell with a lower capacity could become a liability, drawing energy from its peers and becoming a potential point of failure.

Deep Dive into Battery Types

Beyond the realm of basic cell combinations, batteries can be differentiated based on their chemical makeup. This distinction dictates their voltage, capacity, longevity, and ideal use-cases.

Lithium-ion (Li-ion):

Popular in smartphones and EVs, these batteries offer high energy density and can be recharged multiple times without significant capacity loss.

Nickel-Metal Hydride (Ni-MH):

Often found in household electronics, they offer a good balance between cost and performance.


The old guards of the battery world, they're primarily used in vehicles for starting, lighting, and ignition (SLI) purposes.


Common in disposable batteries for gadgets like TV remotes. They have a long shelf life but aren't ideal for high-drain devices.


The memory effect refers to a phenomenon observed in some rechargeable batteries, particularly older nickel-cadmium (NiCd) cells, where they "remember" a particular discharge level and struggle to maintain a charge beyond that point. It occurs if the battery is repeatedly recharged without being fully discharged. Over time, this results in reduced battery capacity. To avoid the memory effect, it's recommended to periodically perform a full discharge followed by a complete recharge, ensuring the battery utilises its full capacity range. However, note that many modern batteries, like Lithium-ion, aren't prone to this effect.

Batteries are tailored to cater to different applications and requirements. Factors like voltage, capacity, size, weight, and discharge rate influence battery design. For instance, a watch needs a tiny, long-lasting battery, while a camera flash might require a larger battery with a rapid discharge rate. Because of these specific needs, we have a plethora of battery types. While some batteries might physically fit into different devices, interchanging them isn't advisable. Using an incorrect battery can lead to inadequate performance, potential damage, or safety risks. Always follow manufacturer guidelines when selecting batteries.

When devices are not in use, there can still be a minute current drain from the battery, leading to a gradual loss of charge. Over time, if batteries are excessively discharged, they can get damaged or leak. Battery leakage can corrode and damage the device's internals. By removing the battery from devices that aren't in use for long durations, you prevent potential damage to both the battery and the device.

Temperature has a pronounced effect on battery performance. At low temperatures, the chemical reactions in batteries can become sluggish, leading to reduced energy output. This is why a car battery might struggle to start on an exceptionally cold morning. Conversely, at high temperatures, the rate of undesirable chemical reactions can increase, potentially shortening the battery's lifespan. Overheating can also lead to thermal runaway, a dangerous condition where internal battery temperatures surge uncontrollably, potentially resulting in fires or explosions in extreme cases.

All batteries have a finite life, which is influenced by chemical reactions occurring within them. Over time, undesired side reactions can take place, leading to the build-up of insulating layers or causing structural changes within the battery components. For rechargeable batteries, every charge-discharge cycle induces a bit of wear and tear, causing slight reductions in their capacity. This cumulative degradation reduces the battery's ability to hold a charge, leading to a diminished capacity over time. Though they're designed for repeated use, even rechargeable batteries will reach a point where they can't efficiently store energy, causing them to "die."

Practice Questions

An electric vehicle (EV) employs a battery pack designed with cells arranged in both series and parallel. Explain how this combination serves to meet the vehicle’s energy requirements and provide an advantage over using only one type of arrangement.

Electric vehicles necessitate a high voltage for optimal performance, as well as a large capacity to ensure a longer driving range between charges. By using cells in a series configuration, the total voltage of the battery pack is increased, enhancing the EV's performance. Concurrently, a parallel configuration of cells bolsters the total capacity, providing the vehicle with extended endurance. Thus, an EV battery pack combines both series and parallel configurations to harness the benefits of elevated voltage and augmented capacity. This dual configuration offers a significant advantage over solely using one type, enabling the vehicle to perform optimally while also ensuring a practical driving range.

Among the various types of batteries discussed, Lithium-ion (Li-ion) batteries are prevalent in smartphones. Elucidate the reasons behind the ubiquity of Li-ion batteries in such devices, considering their properties and the requirements of smartphones.

Smartphones demand batteries that are lightweight, compact, and can store a substantial amount of energy. Lithium-ion batteries fit the bill perfectly as they possess a high energy density, meaning they can store more energy for their size compared to other battery types. Additionally, Li-ion batteries have a relatively low self-discharge rate, ensuring that smartphones retain charge over extended periods when not in use. They can also endure numerous charge-discharge cycles without significant capacity loss, which is pivotal given the frequent charging habits of typical smartphone users. Hence, given their high energy density, longevity, and adaptability to regular charging, Li-ion batteries have become the go-to choice for smartphone manufacturers.

Dr Shubhi Khandelwal avatar
Written by: Dr Shubhi Khandelwal
Qualified Dentist and Expert Science Educator

Shubhi is a seasoned educational specialist with a sharp focus on IB, A-level, GCSE, AP, and MCAT sciences. With 6+ years of expertise, she excels in advanced curriculum guidance and creating precise educational resources, ensuring expert instruction and deep student comprehension of complex science concepts.

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