---
title: "Cells That Do Work: Batteries, Fuel Cells and Corrosion"
description: "A cell potential is only a prediction until current flows and the cell has to keep supplying it. Rechargeable cells, fuel cells and a rusting car body are all the same electrochemistry read in differe"
canonical: https://lightmysky.com/learn/science/cells-that-do-work-batteries-fuel-cells-and-corrosion-mt_NQQzlecX4v
source: https://lightmysky.com/learn/science/cells-that-do-work-batteries-fuel-cells-and-corrosion-mt_NQQzlecX4v.md
retrieved: 2026-09-12
---

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# Cells That Do Work: Batteries, Fuel Cells and Corrosion

A cell potential is only a prediction until current flows and the cell has to keep supplying it. Rechargeable cells, fuel cells and a rusting car body are all the same electrochemistry read in different directions.

Subject: Science · Area: Chemistry · Ages 17 to 18
Page: https://lightmysky.com/learn/science/cells-that-do-work-batteries-fuel-cells-and-corrosion-mt_NQQzlecX4v

## Ready when they can

- Write the electrode reactions for a familiar rechargeable cell in both charge and discharge directions
- Explain what a fuel cell does differently from a battery, and what limits its voltage
- Account for rusting as an electrochemical process and explain why sacrificial protection works

## Lesson: Batteries, fuel cells, and rust

A battery is a galvanic cell engineered so its spontaneous reaction delivers a steady, useful current. The voltage on paper only predicts what the cell could give. A working cell must keep supplying current, so its voltage sags as reactants run out and dips further under a heavy load.

Batteries come in two families. Primary cells, like the alkaline cells in a flashlight, run once and are thrown away. Secondary cells, like the lead-acid battery in a car or the lithium-ion cell in a phone, recharge because driving current backward reverses the electrode reactions. In a lead-acid cell, discharge turns lead and lead dioxide into lead sulfate, and charging pushes that change in reverse. Side reactions still wear rechargeables out over hundreds of cycles.

A fuel cell skips storage entirely. It is fed fuel and oxidizer from outside, usually hydrogen and oxygen, and it runs as long as fuel keeps flowing, giving water as the product. It never needs recharging, but it always needs a fuel supply. Its real voltage falls short of the ideal because electrode reactions are slow and the cell resists current, so engineers stack many cells for useful voltages.

**Example.** Now read a rusting nail as the same story in the wrong place. Rust is electrode chemistry running as a stray, unwanted cell on the metal surface. Sacrificial protection bolts on a second metal that takes the corrosion instead, so the nail you care about is spared. Battery, fuel cell, and rust are one chemistry read in three directions.

**Recap.** Batteries store reactants, fuel cells are fed, and rust is the same chemistry unwanted.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Electrolysis: Half Equations at the Electrodes](https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY)
- [Standard Electrode Potentials and Predicting Redox Reactions](https://lightmysky.com/learn/science/standard-electrode-potentials-and-predicting-redox-reactions-mt_LDI10CjoAI)
- [Free Energy and Whether a Reaction Is Feasible](https://lightmysky.com/learn/science/free-energy-and-whether-a-reaction-is-feasible-mt_o1kZgBYWoM)

## Opens up

- [The Nernst Equation and Cells Away from Standard Conditions](https://lightmysky.com/learn/science/the-nernst-equation-and-cells-away-from-standard-conditions-mt_yqmRqDaadR)