Battery Fundamentals

Battery 101 — a technical reference series on how a lithium pack is built, measured and worn out. Written for engineers and pack integrators, but starting in plain language at every step.

3 chapters published

How to read this series

Each chapter starts in plain language and ends with real equations, worked examples and questions to test yourself. No prior background is assumed — but nothing is hand-waved either. Chapters build on each other, so reading in order pays off, though each is written to stand alone.

Part 1

Anatomy and Instrumentation

What a lithium pack is physically made of, what the protection board watching over it actually does, and how a pack is put on the bench and measured.

124 min read

Inside the Battery: the BMS and the Cell

How a software-defined protection board and a 100Ah LiFePO4 prismatic cell work together to keep a lithium pack safe, efficient and long-lived.

Every lithium pack is two products in one: a chemical energy store and a digital nervous system watching over it. This chapter takes both apart — the four pillars of BMS protection (voltage, current, temperature, balance) with real threshold tables, coulomb counting and sleep behaviour, the full connector pinout, the cell’s own electrical and safety test criteria, and a side-by-side map of where the board’s trip points sit relative to the cell manufacturer’s stated limits.

BMS protectionLiFePO4 cell specCell balancingSafety testing

Read chapter 1

212 min read

Active Balancing & Capacity Test Procedure

A charge → active balance → discharge workflow for a series lithium pack, using a bench balancer/analyser to equalise every cell and measure each cell’s real delivered capacity.

The bench counterpart to Chapter 1. This chapter is a working procedure: the equipment class involved, the safety precautions that come first, five phases running from harness connection through charge, active cell-to-cell balancing and a controlled discharge capacity test, with worked example convergence and per-cell capacity data, pass/fail interpretation and a troubleshooting quick reference.

Active balancingCapacity testingWeak cell detectionBench procedure

Read chapter 2

Part 2

State, Health and Degradation

The numbers a pack reports about itself — state of charge, depth of discharge, state of health — what they really mean, how they relate, and what wears a battery out over its life.

334 min read

Depth of Discharge, Capacity, SoC, SoH & Battery Degradation

The core state metrics that govern every lithium pack — what each one means, how they relate to one another, and what actually wears a battery out.

A first-principles guide to the numbers a pack reports about itself. This chapter separates capacity (how big the battery is) from state of charge (how full it is right now) and depth of discharge (how big a swing a cycle takes), derives why DoD is the dominant driver of cycle life, defines state of health in both its capacity and resistance forms, works through the electrochemical mechanisms behind degradation, and answers directly whether DoD is a matter of voltage, capacity or resistance. It closes with a full worked comparison of 16S and 20S 100Ah LiFePO4 packs, and with the practical question behind all of it: to hold a pack to 60% DoD, which BMS setting do you actually change?

State of chargeDepth of dischargeState of healthDegradationSetting a DoD limit

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More chapters are being written. This is an open-ended reference series — new chapters are added as topics come up in real pack design, testing and field work.