Development of Automatic 18650 Battery Capacity Tester

Abstract

This thesis presents the design and implementation of an automatic 18650 battery capacity tester, offering a cost-effective and precise solution for evaluating battery performance. The project integrates theoretical research on lithium-ion batteries with practical engineering to develop a system featuring adaptive constant current (CC) discharge algorithms, internal resistance (IR) testing, real-time thermal monitoring, and serial communication for data visualization. Key innovations include a smart adaptive discharge mechanism that dynamically adjusts current based on voltage feedback, ensuring high measurement accuracy, and a DC load method for IR measurement with ±1.5% error margins.

The methodology involved rigorous testing of the system using Samsung and Sony 18650 cells across 50 charge-discharge cycles. Results demonstrated a voltage measurement accuracy of ±0.07V, IR consistency within ±1.4mΩ, and a total system cost under €50, outperforming commercial testers in functionality and affordability. The open-source design, modular firmware, and compatibility with multiple battery chemistries make this tester a scalable tool for hobbyists, researchers, and recyclers. By bridging the gap between academic research and real-world applications, the project delivers a reliable and accessible solution for comprehensive battery diagnostics.