Title: Module 1: Battery Construction & Types - Lesson
Course: ASE A6 Battery Service > Section: Module 1: Battery Construction & Types

Objectives

By the end of this module, students will be able to:

1. Identify the major internal and external components of a lead-acid battery
2. Explain the function of each component within the battery assembly
3. Describe how cells are connected in series to produce 12.6 volts
4. Distinguish between flooded, AGM, gel, and spiral wound battery designs
5. Read and interpret battery ratings (CCA, CA, RC, Ah)

ASE A6 Alignment

Module 1 provides the foundational knowledge required for all ASE A6 battery service tasks. Understanding battery construction, types, and ratings is prerequisite knowledge for testing, charging, maintenance, and diagnosis.

Introduction

The lead-acid battery has been powering vehicles since the early 1900s. Despite advances in lithium-ion and other chemistries, the flooded lead-acid and AGM battery remain the dominant starting battery in conventional vehicles. Understanding how these batteries are built is the foundation for everything that follows — testing, charging, maintenance, and diagnosis all depend on knowing what is inside the box.

In this module, you will disassemble and reassemble the 3D printed battery model, identifying each component and connecting it to its real-world counterpart.

Battery Overview

A standard automotive battery is a 12-volt lead-acid battery consisting of 6 cells connected in series. Each cell produces approximately 2.1 volts, giving a fully charged total of 12.6 volts.

Each cell contains:

- Positive plates coated with lead dioxide (PbO2)
- Negative plates coated with sponge lead (Pb)
- Separators between each plate to prevent short circuits
- Electrolyte — a mixture of sulfuric acid (H2SO4) and water

External Components

Battery Case

The case is the outer housing of the battery. It is made of polypropylene plastic — a material chosen for its resistance to sulfuric acid, vibration, and temperature extremes.

Key features:

- Cell partitions — Internal walls divide the case into 6 separate cell compartments
- Sediment space — A raised ridge at the bottom of each cell keeps plates off the floor, preventing short circuits from fallen plate material
- Hold-down ledge — A flange or recess where the battery hold-down clamp secures the battery to the vehicle tray

3D Battery Component: The case component represents the outer housing. Notice the 6 internal compartments visible through the acrylic front panel.

Battery Top (Cover)

The cover seals the top of the battery and contains:

- Terminal posts — Two posts (positive and negative) protruding through the cover for external connections
- Vent caps or sealed valves — Older flooded batteries had removable caps for electrolyte service; most modern automotive batteries are sealed "maintenance-free" designs with pressure relief valves only
- Fill holes — Present on older serviceable flooded batteries; most current production batteries do not have accessible fill holes

3D Battery Component: The top is secured with four hold-down screws.

Terminal Posts

The battery has two terminal posts:

- Positive post (+) — Slightly larger in diameter, often marked with a "+" and/or red color
- Negative post (-) — Slightly smaller, marked with a "-" and/or black color

The size difference is intentional — it prevents connecting cables to the wrong terminal.

3D Battery Component: The positive-post and negative-post components are different colors to match the real-world convention.

Hold-Down Hardware

Batteries must be secured in the vehicle to prevent:

- Vibration damage to internal plates
- Movement during collisions
- Terminal contact with the hood or other metal

3D Battery Component: Four hold-down screws with thumb wheels fasten the top to the case, simulating the hold-down clamp system.

Internal Components

Plate Grids

The plate grid is a lead-alloy framework that serves two purposes:

1. Structural support — Holds the active paste material in place
2. Current conductor — Carries electrical current to and from the active material

Grids are made from lead alloyed with antimony, calcium, or tin to improve strength and reduce corrosion. The grid pattern creates a lattice of open spaces that the active paste fills.

3D Battery Component: The positive-plate-grid and negative-plate-grid components show the lattice structure. In Bambu Studio, these are multi-color prints — use "individual objects" painting mode, not default auto-painting.

Active Material (Plate Paste)

The paste applied to each grid determines whether it functions as a positive or negative plate:

Plate | Active Material | Chemical Formula | Color
Positive | Lead dioxide | PbO2 | Dark brown/chocolate
Negative | Sponge lead | Pb | Gray

Each cell contains one more negative plate than positive. This means the outermost plates on both sides of the plate group are negative, which improves efficiency by ensuring every positive plate has a negative plate on both sides.

3D Battery Component: Positive-plate-paste (12 per battery) and negative-plate-paste (24 per battery) snap onto their respective grids. Notice there are twice as many negative paste components.

Separators

Separators are thin, porous sheets placed between every positive and negative plate. They serve a critical dual function:

1. Electrical insulation — Prevent direct contact (short circuit) between positive and negative plates
2. Ion permeability — Allow sulfate ions to pass freely through the electrolyte during charge and discharge

In flooded batteries, separators are typically microporous polyethylene. In AGM batteries, separators are absorbent glass mat — a fiberglass material that also holds the electrolyte in place.

3D Battery Component: The separator is printed in TPU (flexible material) and consists of two halves that join together, representing the porous barrier between plates. Six full separators are used per battery (printed as 12 halves).

Electrolyte

The electrolyte is a solution of sulfuric acid (H2SO4) and water (H2O). It serves as the chemical medium that enables the transfer of ions between positive and negative plates during charge and discharge.

Key facts:

- Fully charged specific gravity: 1.265
- Fully discharged specific gravity: 1.120
- The acid concentration changes as the battery charges and discharges — acid is consumed during discharge and regenerated during charging

3D Battery Component: Six colored electrolyte containers represent the 6 cells. Each is printed in translucent PETG to suggest the liquid nature of the electrolyte. Educational labels on each cell teach specific battery concepts.

Intercell Connectors (Cell Straps)

The 6 cells are connected in series using intercell connectors called cell straps. Each strap connects the positive plate group of one cell to the negative plate group of the adjacent cell.

Series connection means voltages add:

- 1 cell = 2.1V
- 6 cells in series = 2.1V x 6 = 12.6V

The first and last cells connect to the external terminal posts.

3D Battery Component: Five cell straps connect the 6 cells in series. The acrylic front panel lets you see how they bridge between cell compartments.

Battery Types

Flooded (Conventional) Lead-Acid

- Liquid electrolyte freely covers the plates
- Produces hydrogen gas during charging — must be vented
- Least expensive battery type
- Older designs had removable vent caps for adding water; most modern flooded batteries are sealed "maintenance-free" and do not allow electrolyte service
- Still used in many vehicles, but increasingly replaced by AGM in newer platforms

AGM (Absorbent Glass Mat)

- Electrolyte absorbed into fiberglass mat separators
- Sealed design with pressure relief valves
- No free liquid — spill-proof, mountable in any orientation
- Lower internal resistance — better for high-current applications
- Higher cost than flooded
- No electrolyte access — cannot check specific gravity with a hydrometer

Gel Cell

- Electrolyte mixed with silica to form a gel
- Sealed, maintenance-free
- Very sensitive to overcharging — requires precise voltage control
- Primarily used in deep-cycle applications (wheelchairs, solar)
- Not common in automotive starting applications

Spiral Wound (Optima-style)

- Plates wound in a spiral rather than stacked flat
- Very low internal resistance, high vibration tolerance
- Sealed AGM design
- Premium cost
- Popular in off-road, racing, and dual-purpose applications

Battery Ratings

Rating | Full Name | Definition
BCI Group Size | Battery Council International Group Size | Standardized number (e.g., 24, 34, 65, 78) that defines the battery's physical dimensions, terminal location, and polarity — ensures the battery fits the vehicle's tray and hold-down
CCA | Cold Cranking Amps | Amps the battery can deliver for 30 seconds at 0°F (-18°C) while maintaining at least 7.2V
CA | Cranking Amps | Same test at 32°F (0°C) — always higher than CCA
RC | Reserve Capacity | Minutes the battery can deliver 25 amps at 80°F before dropping below 10.5V
Ah | Amp-Hours | Total capacity — amps x hours at a 20-hour discharge rate

The BCI group size does not indicate performance — it tells you the physical size and terminal configuration. Its location on the label varies by manufacturer — it may appear alongside the performance ratings or in a separate area of the label. When replacing a battery, the group size must match to ensure proper fit in the tray and compatibility with the hold-down and cables.

CCA is the most commonly referenced performance rating for automotive starting batteries. A higher CCA means the battery can deliver more current in cold weather to crank the engine.

Key Takeaways

1. A 12V automotive battery contains 6 cells in series, each producing 2.1V
2. Each cell has positive plates (PbO2), negative plates (Pb), separators, and electrolyte (H2SO4 + H2O)
3. There is always one more negative plate than positive in each cell
4. The case, cover, posts, and hold-down hardware make up the external structure
5. Battery types differ primarily in how the electrolyte is contained — liquid (flooded), absorbed (AGM), or gelled (gel)
6. CCA is the primary rating for automotive starting batteries

Vocabulary

Term | Definition
Active material | The chemical paste on a plate grid that participates in the electrochemical reaction
BCI group size | Battery Council International standardized number defining physical dimensions, terminal location, and polarity
Cell | One unit of a battery containing positive plates, negative plates, separators, and electrolyte; produces ~2.1V
CCA | Cold Cranking Amps — current capacity at 0°F
Electrolyte | Sulfuric acid and water solution enabling ion transfer between plates
Grid | Lead-alloy lattice that supports active material and conducts current
Plate group | All positive or all negative plates in one cell, connected by a strap
Separator | Porous barrier between plates that prevents shorts while allowing ion flow
Series connection | Linking cells positive-to-negative so voltages add together
Specific gravity | Density of electrolyte compared to water; indicates state of charge

Dual-Battery Systems

Large diesel engines often require two 12V batteries wired in parallel to deliver enough cranking amps to start the engine. The batteries are connected positive-to-positive and negative-to-negative, so the system voltage stays at 12V while cranking capacity doubles.

Dodge Ram with Cummins turbo diesel — large diesel engines often require two 12V batteries wired in parallel to supply enough cranking amps to start the engine

Parallel wiring connects positive to positive and negative to negative — voltage stays at 12V while cranking capacity doubles