Battery packs and cells are two fundamental concepts in battery systems, differing significantly in structure, function, and application.
1. Basic Concepts
A cell is the smallest functional unit of a battery system, the basic building block of a battery pack. Cell types include lithium-ion cells, nickel-metal hydride cells, and lead-acid cells, each containing components such as a positive electrode, negative electrode, electrolyte, and separator.

A battery pack is a more complex battery system composed of multiple cells connected in series, parallel, or a combination thereof. Battery packs typically include a battery management system (BMS), protection circuitry, and a casing, providing higher voltage or capacity to meet specific application requirements.

2. Structural Differences
A cell has a relatively simple structure, typically cylindrical, prismatic, or pouch-type. A battery pack, on the other hand, is a modular structure composed of multiple cells encapsulated within a common casing, which may include a cooling system, control circuitry, and other auxiliary equipment.

3. Functional Differences
The function of a cell is to store and release electrical energy; it is the site of the battery's chemical reactions. In addition to storing and releasing electrical energy, battery packs also use a Battery Management System (BMS) to monitor and manage the battery cells, including but not limited to monitoring voltage, current, and temperature, as well as providing equalization charging and overcharge/over-discharge protection.

4. Application Scenarios
Battery cells are typically used as components of a battery pack, not individually, but can be used in some low-power devices. Battery packs are widely used in electric vehicles, portable electronic devices, energy storage systems, aerospace, and other fields, providing the necessary voltage and capacity to drive or power these devices.

5. Performance Characteristics
The performance characteristics of a battery cell include its rated capacity, nominal voltage, internal resistance, and charge/discharge rate. The performance of a battery pack is affected by the performance of its constituent cells, the connection method, and the performance of the BMS. The overall performance of a battery pack is often higher than that of a single cell, especially in terms of reliability and flexibility.

6. Manufacturing and Cost
The manufacturing of battery cells is relatively simple and inexpensive. The manufacturing of battery packs is more complex, requiring consideration of cell consistency, thermal management, mechanical stability, and electrical protection, thus resulting in higher costs.

7. Safety
The safety of a battery cell primarily depends on its chemical properties and physical structure. Battery pack safety is more complex, encompassing not only the safety of the cells themselves but also the protection functions of the BMS, the effectiveness of the thermal management system, and the overall structural stability.

8. Technological Development Trends
Cell technology is evolving towards increasing energy density, reducing costs, and improving safety and cycle life. Battery pack technology is continuously progressing in areas such as increasing integration, optimizing BMS algorithms, enhancing thermal management capabilities, and improving overall performance.

9. Maintenance and Recycling
Battery cells typically require no user maintenance, while battery packs may require periodic maintenance, such as checking BMS functionality and replacing coolant. Battery pack recycling is more complex, requiring specialized dismantling and processing techniques.

10. Summary
Battery packs and cells play different roles in a battery system. Cells are the foundation of a battery pack, while the battery pack integrates and applies the cells.