Cells and batteries form the foundation of automotive electrical systems, powering everything from engine ignition to lighting and infotainment. For automotive engineering technologists in Kenya, understanding how these energy storage devices work is essential for diagnosing electrical issues and ensuring vehicle reliability. This chapter explores the fundamental principles and practical applications of cells and batteries, enabling technicians to select, maintain, and troubleshoot them effectively in diverse automotive environments.

3.1 Introduction to Cells and Batteries

3.1.1 Definition and Basic Concepts of Cells and Batteries

A cell is a single electrochemical unit that converts chemical energy into electrical energy through redox reactions. Cells have two electrodes: the anode (negative) and cathode (positive), separated by an electrolyte which facilitates ion movement. A battery consists of two or more cells connected in series or parallel to provide the desired voltage and current capacity.

• Cells produce voltage by chemical reactions between electrodes and electrolyte.
• Electrolytes can be liquid, gel, or solid, affecting the cell’s performance and maintenance.
• Batteries aggregate cells to increase voltage (series) or capacity (parallel).
• Automotive batteries typically provide 12 volts-made up of six 2-volt cells connected in series.
• The effectiveness of a battery depends on the chemical composition, cell design, and usage conditions.

3.1.2 Types of Cells Used in Automotive Batteries

Automotive applications predominantly use two types of cells: lead-acid and lithium-ion, each with distinct characteristics affecting performance and maintenance.

• Lead-acid cells are the most common in conventional vehicles due to their cost-effectiveness and reliability. They use lead dioxide and sponge lead as electrodes with sulfuric acid as electrolyte.

Woman testing a lead-acid cell battery (Source: Wikimedia Commons)

• Lithium-ion cells are increasingly used in electric vehicles (EVs) for their higher energy density, lighter weight, and longer cycle life.

Two cylindrical lithium-ion cells in holders (Source: Wikimedia Commons)

• Nickel-metal hydride (NiMH) cells appear in hybrid vehicles, balancing cost and capacity.

AAA size nickel-metal hydride rechargeable battery cell (Source: Wikimedia Commons)

• Sealed cells (VRLA - Valve Regulated Lead Acid) prevent electrolyte leakage and require minimal maintenance.
• Flooded cells require regular electrolyte level checks and are more sensitive to temperature variations.

3.1.3 Construction and Components of Automotive Batteries

Understanding the internal structure of automotive batteries helps in diagnostics and maintenance. The key components include:

• Positive plates made of lead dioxide in lead-acid batteries, which act as the cathode.

• Negative plates made of spongy lead, serving as the anode.

• Electrolyte consisting of sulfuric acid diluted with water, facilitating ion transfer.

• Separators that prevent physical contact between positive and negative plates while allowing ionic movement.

• Battery casing made from durable plastic to contain the chemical components and provide mechanical protection.

• Terminals for electrical connection to the vehicle’s system.

3.1.4 Role of Cells and Batteries in Vehicle Electrical Systems

Batteries are central to vehicle operation, providing power for starting, lighting, and ignition (SLI), as well as stabilizing voltage for sensitive electronics.

• Batteries supply high current to the starter motor to crank the engine.
• They provide power when the alternator output is insufficient, such as during engine idle.
• Batteries stabilize voltage and filter electrical noise, protecting electronic control units (ECUs).
• In hybrid and electric vehicles, batteries serve as the primary energy source for propulsion.
• Proper battery performance is critical for safety features like airbags and ABS systems.

Chapter Summary

This chapter introduces the fundamental concepts of cells and batteries, focusing on their role in energy storage through electrochemical cells. It explains key electrical properties such as voltage, current, capacity, and energy density, alongside the internal resistance and electromotive force that influence cell performance. The electrochemical principles of redox reactions and electrode potentials are detailed, as well as the essential components of a cell including the anode, cathode, electrolyte, and separator. Distinctions between primary non-rechargeable cells and secondary rechargeable cells are explored, with specific attention to zinc-carbon, alkaline, and lithium primary cells, followed by lead-acid, nickel-cadmium, nickel-metal hydride, and lithium-ion batteries. The chapter also covers battery performance factors such as capacity, temperature effects, internal resistance, state of charge, and aging mechanisms, complemented by techniques for measuring and testing battery health. Applications of batteries across consumer electronics, automotive, electric vehicles, industrial storage, and renewable energy systems are discussed, highlighting associated challenges and standards. Finally, the environmental impact of batteries is examined, including disposal concerns, recycling methods, government regulations, and advances in eco-friendly technologies.