18650 Li-ion Internal Resistance Explained & Measured

About this Video

• Video Title: 18650 Li-ion Internal Resistance Explained & Measured
• Channel: Tom Donnelly
• Speakers: Tom Donnelly
• Duration: 00:08:42

Introduction

This video explains 18650 Li-ion battery internal resistance and demonstrates how to measure it. The speaker highlights the importance of measuring internal resistance to assess battery health and lifespan, explaining the impact of factors like cell capacity and discharge rates. He details a manual measurement method using Ohm's Law and Kirchhoff's Voltage Law.

Key Takeaways

• Internal Resistance Explained: A battery's internal resistance is the combined resistance of the materials within the cell through which electrons flow to release energy. Higher internal resistance indicates reduced performance and battery degradation.
• Measuring Internal Resistance: The speaker demonstrates a manual method to measure internal resistance using a voltmeter, resistor, Ohm's Law (V=IR), and Kirchhoff's Voltage Law. The process involves measuring open voltage, voltage with a resistor, calculating current, determining voltage drop, and finally, calculating internal resistance.
• Battery Health Indicator: Internal resistance is a key indicator of a battery's health. Increased internal resistance signifies degradation due to the buildup of a solid electrolyte interface (SEI) layer on the anode.
• Extending Battery Life: Lowering the cut-off voltage on charge by 0.1 volts (e.g., from 4.2V to 4.1V) can help extend battery life by reducing SEI buildup. High-capacity cells especially benefit from this practice.
• Consistent Measurement: For accurate comparisons, measure internal resistance at the same voltage each time (preferably nominal or fully charged voltage, but not exceeding 4.1V).