Battery Cells, Battery Modules, and Battery Packs: A Comprehensive Analysis from Basic Units to System Assemblies

Drone Battery

ENOV High-Energy drone batteries power industrial and commercial drones. Delivering 220–320 Wh/kg energy density, they enable long flight times (30+ mins) and support fast charging (2C). Perfect for aerial photography, surveillance, and delivery drones.

In modern energy storage systems, battery cells, battery modules, and battery packs form a three-tier structure ranging from basic energy storage units to end-use application systems. These three differ significantly in terms of integration level, functional positioning, and application scenarios, yet they are closely interconnected. Together, they meet the energy demands of various devices such as electric vehicles, energy storage power stations, and consumer electronic products. Below is a detailed analysis of the differences and connections among the three from the perspectives of definition, core characteristics, typical types, and applications.

1. Battery Cell: The Basic Minimum Unit of the Energy Storage System

A battery cell serves as the core carrier for converting chemical energy into electrical energy. It is the smallest indivisible unit in a battery system that possesses independent energy storage capabilities, and the performance of all battery systems is built on this foundation.

(1) Core Composition

Each battery cell consists of five key components, each with a distinct and indispensable function:

• Positive and Negative Electrodes: These act as storage spaces for lithium ions. Common materials used for the positive electrode include lithium cobalt oxide, nickel-cobalt-manganese, and lithium iron phosphate, while graphite is widely adopted for the negative electrode.

• Electrolyte: It functions as a “channel” for the movement of lithium ions between the positive and negative electrodes, ensuring the smooth progress of electrochemical reactions.

• Separator: It has both “isolation” and “conduction” functions. It can prevent direct contact between the positive and negative electrodes, which would otherwise cause a short circuit, and at the same time, allow lithium ions to pass through.

• Shell: It provides physical protection and sealing for the internal components. The shell materials of different types of battery cells vary greatly. For example, cylindrical batteries use metal shells, and pouch batteries use aluminum-plastic films.

(2) Key Characteristics

• Fixed Parameters: The voltage, capacity, and size of a battery cell are determined by its material system and cannot be adjusted arbitrarily. For instance, the voltage of a ternary lithium battery cell is usually 3.7V, and that of a lithium iron phosphate battery cell is approximately 3.2V. In terms of capacity, a 18650 cylindrical cell has a capacity of about 2-3.4Ah, a 21700 cylindrical cell can reach a capacity of 4-5Ah, and the capacity of a prismatic cell is more flexible with changes in size, ranging from 20Ah to 560Ah.

• Weak Independence: When used alone, a battery cell can only provide low voltage and small capacity, which is unable to meet the high-power requirements of most devices. For example, a single 18650 cell can only power a small LED light, and it needs to be combined with other cells to serve devices with higher power demands.

(3) Typical Types and Their Characteristics

Currently, the mainstream battery cells are mainly divided into three types: cylindrical, prismatic, and pouch. Each type has its own focus in terms of structure, performance, and applicable scenarios.

Type	Structural Characteristics	Advantages	Disadvantages	Typical Applications
Cylindrical Battery	The positive electrode, negative electrode, and separator are wound into a cylindrical shape and placed in a metal shell.	Mature manufacturing process, high degree of automation, and low cost; uniform internal stress distribution and good mechanical strength; high standardization level, allowing interchangeability of products from different manufacturers; large surface area-to-volume ratio and excellent heat dissipation.	Low space utilization, with gaps easily formed in rectangular spaces; small single-cell capacity, requiring a large number of series/parallel connections to build a high-capacity system, resulting in complex assembly; fixed size and poor design flexibility.	Power tools, portable devices, electric vehicles (e.g., Tesla).
Prismatic Battery	It adopts a hard shell made of aluminum or steel, with a wound or stacked internal structure.	Rectangular structure ensures high space utilization, which is beneficial for improving the energy density of the battery pack; large single-cell capacity reduces the number of series/parallel connections and simplifies the system design; large contact surface facilitates heat dissipation and heat management	Higher manufacturing cost than cylindrical batteries and stricter requirements for the production process; prone to expansion during charge-discharge cycles, requiring additional reserved space and mechanical constraints; large differences in specifications among different manufacturers, leading to poor interchangeability.	Electric vehicles (e.g., BYD, CATL), commercial electric vehicles, energy storage systems.
Pouch Battery	It uses an aluminum-plastic film as the shell, with a mostly stacked internal structure.	Light weight and high gravimetric energy density; extremely high design flexibility, allowing customization of size and shape according to requirements; low internal resistance and good rate performance; in case of thermal runaway, pressure is mostly released through expansion, resulting in relatively controllable safety.	Low mechanical strength of the aluminum-plastic film, making it vulnerable to external damage and requiring additional protective structures; high environmental requirements for production, especially sensitivity to moisture, and sealing must be carried out in a dry environment; needs to be protected against pressure and moisture during storage and transportation, leading to high logistics costs; low production yield and weak cost competitiveness.	Consumer electronic products (e.g., smartphones, laptops, tablets), portable devices.

2. Battery Module: The "Integrated Group" of Battery Cells

A battery module is an intermediate integrated unit formed by connecting multiple battery cells in series or parallel according to requirements and equipping them with auxiliary structures such as protection, fixation, and heat dissipation components. Its core function is to address the issue of insufficient voltage and capacity of a single battery cell, while ensuring the consistency and safety of the cells, and providing a standardized “module unit” for the subsequent integration of battery packs.

(1) Core Composition

A battery module is centered on “battery cells + auxiliary structures”. The auxiliary structures include four major categories, which together ensure the stable operation of the module:

• Mechanical Structure: Such as metal or plastic brackets and end plates. These are used to fix the positions of the battery cells, prevent collisions, and the end plates can also provide a certain pressure for the cells to maintain the structural stability of the module.

• Electrical Protection: It includes fuses and contactors, which can prevent overcurrent and short circuits of the cells and avoid the expansion of electrical faults.

• Thermal Management Structure: For example, heat sinks, thermal pads, cooling plates, and cooling pipes. These are used to balance the temperature of the cells, prevent local overheating, and ensure that the module operates within an appropriate temperature range.

• Monitoring Module: Such as voltage sampling lines and temperature sensors. These can monitor the voltage and temperature of each cell in real-time, providing data support for consistency management and fault early warning.

(2) Key Characteristics

• Moderate Integration Level and Connecting Function: Downwardly, it “groups” the scattered battery cells. By connecting the cells in series, the voltage is increased, and by connecting them in parallel, the capacity is increased. For example, 24 units of 3.7V cells connected in series can output a voltage of approximately 88.8V. Upwardly, it provides standardized components for the battery pack, simplifying the assembly process and later maintenance of the battery pack, and reducing the difficulty of system integration.

• Consistency as the Core Lifeline: The battery cells within a module must undergo strict “screening and matching” to ensure minimal errors in voltage, capacity, and internal resistance. If the consistency of the cells is poor, the “barrel effect” will occur-a certain cell will decay prematurely, directly leading to the failure of the entire module. Therefore, the screening process is a crucial step in module production.

(3) Typical Applications

• Core Component of Power Batteries: It is a key part of the battery pack of electric vehicles. For example, the battery pack of the early version of Tesla Model 3 is composed of 4 modules, and the series/parallel connection of the modules realizes the voltage and capacity required by the entire vehicle.

• Intermediate Layer of Energy Storage Systems: Household energy storage power stations usually adopt a combination of 2-4 modules, which can be flexibly adjusted according to the user’s power needs to adapt to different household electricity scenarios.

• Other Medium-Power Devices: Some power tools and small-sized commercial devices also use modules as energy supply units to balance power requirements and costs.

3. Battery Pack: The System-level Energy Assembly for End-use Applications

A battery pack (also known as a “battery case”) is a “final application system” formed by integrating multiple battery modules, a complete set of control systems, and a shell. It is the “finished form” of the battery system and can directly provide stable and safe electrical energy for end-use devices. Its design must be fully adapted to the needs of the end-use devices.

(1) Core Composition

A battery pack has the highest integration level and consists of three core parts. These parts work together to ensure the safe and efficient operation of the system:

• Energy Main Body: It is composed of multiple battery modules connected in series or parallel. Series connection is used to increase the voltage, and parallel connection is used to increase the capacity. For example, 10 modules of 88.8V connected in series can output a voltage of approximately 888V, meeting the high-voltage requirements of high-end electric vehicles. Some battery packs using CTP (Cell to Pack) technology can skip the module level and directly integrate the battery cells, reducing the structural weight and improving the energy density.

• Control System: Centered on the BMS (Battery Management System), it is equivalent to the “brain” of the battery pack. It includes a main controller and multiple slave controllers, forming a hierarchical management structure. The main controller is responsible for system-level management and decision-making, while the slave controllers collect detailed data at the module level. Its core functions include: real-time monitoring of voltage, current, temperature, SOC (State of Charge), and SOH (State of Health); prevention of faults such as overcharging, over-discharging, over-temperature, and short circuits; adjustment of the cell state through active or passive balancing technology to ensure consistency; and accurate estimation of SOC and remaining driving range to provide references for users.

• Auxiliary System: It includes a shell, a thermal management system, a high-voltage power distribution unit, etc. The shell must have waterproof (usually reaching the IP67 protection level), dustproof, and impact-resistant capabilities to protect the internal components. The thermal management system (liquid cooling, air cooling, or phase-change material cooling) is responsible for maintaining the stable temperature inside the pack. In cold environments, it also needs to have a heating function to ensure that the battery operates within the optimal temperature range. The high-voltage interface is used to connect to the power supply end of the device, and the high-voltage power distribution unit is responsible for the distribution and protection of high-voltage electrical energy.

(2) Key Characteristics

• Highest Safety Priority: A battery pack must pass strict safety tests, including needle puncture, extrusion, fire, and water immersion tests, to prevent fire and explosion caused by module or cell faults. For example, the power battery pack is specially designed with a “thermal runaway protection” structure, which blocks the spread of thermal runaway through thermal propagation barriers, early warning systems, pressure release devices, etc.

• Full Adaptation to End-use Requirements: The size, weight, voltage, and capacity of a battery pack are all customized according to the needs of the end-use devices. For example, the battery pack of an electric vehicle needs to be adapted to the chassis space and is installed under the chassis using a “skateboard-type” design to lower the center of gravity of the vehicle body. The battery pack of a drone needs to be extremely lightweight to reduce the flight load. The battery pack of an energy storage power station focuses more on capacity and scalability, and most of them adopt a container-type design.

4. The Relationship and Differences Among the Three

(1) Hierarchical Relationship

The three present a clear hierarchy of “from small to large, from basic to system”, with the core being the realization of functional upgrading through gradual integration:

• Basic Layer: A battery cell (single unit) is the smallest energy unit, providing basic energy storage and energy conversion functions.

• Intermediate Layer: A battery module (multiple cells + auxiliary structures) is the “grouped upgrade of cells”. It solves the problem of insufficient performance of a single cell and ensures consistency and initial safety.

• System Layer: A battery pack (multiple modules + control system + shell) is the “system-level finished product of modules”. It integrates the functions of the entire chain, directly connects to end-use applications, and provides stable and safe energy supply.

• Note: With the development of technology, technologies such as CTP (Cell to Pack) and CTC (Cell to Chassis) can skip the module level and directly integrate battery cells into the battery pack or vehicle body, reducing the structural weight and improving the energy density. These technologies have become important development directions in the industry.

(2)Comparison of Core Differences

Comparison Dimension	Battery Cell	Battery Module	Battery Pack
Positioning	Basic energy unit	Intermediate integrated unit	System-level energy assembly
Core Composition	Positive/negative electrodes, electrolyte, separator, shell	Multiple battery cells + brackets + electrical protection + thermal management + monitoring module	Multiple modules + BMS + shell + thermal management system + high-voltage power distribution unit
Voltage/Capacity	Fixed (3.2-3.7V, 2-560Ah)	Increased after cell combination (e.g., 80-100V)	Adapted to requirements after module combination (300-800V, several kWh-hundreds of MWh)
Core Function	Realization of the conversion between chemical energy and electrical energy, and basic energy storage	Enhancement of energy output, ensuring cell consistency, and providing initial safety protection	Stable power supply, full-chain safety protection, and accurate monitoring and management
Typical Applications	Small LED lights, Bluetooth headsets, smart watches	Components of electric vehicle battery packs, household energy storage modules	Electric vehicle battery packs, energy storage power stations, drones

5. Conclusion

Battery cells, battery modules, and battery packs are the core components of an energy storage system. Through a hierarchical structure of “basic unit → intermediate integration → system assembly”, the three achieve a functional leap from “single energy storage” to “adaptation to end-use applications”. Battery cells determine the basic performance of the system, battery modules ensure the stable output and consistency of performance, and battery packs provide a safe and reliable energy solution for devices through full-chain management and control.

With the continuous advancement of technology, the integration methods of the three are constantly optimized. Technologies such as CTP and CTC are reshaping the traditional structure. At the same time, safety, efficiency, cost, and sustainability have become the core goals of the industry’s development. Understanding the characteristics and relationships of the three is of great significance for grasping the direction of energy storage technology and promoting innovation in battery applications.