Safety Design Guide for Series Connection of Button Batteries in Electronic Devices
Ensuring Safety While Maximizing Performance
While the use of multiple button batteries in series is generally not recommended, proper safety design can help maximize battery performance. If you are considering this approach, we strongly encourage you to take advantage of our technical support.
In this article;
1. Introduction
In compact electronic devices, certain applications -- such as LED lighting or motor drives -- require higher voltages or power outputs. To meet these demands, some designs use two or three button batteries, such as SR or LR types, connected in series. However, a series connection of button batteries involves specific risks, and improper design can lead to serious incidents such as leakage or rupture.
This article outlines essential design considerations for safe series use and highlights the benefits of our technical support.
2. Risk of Polarity Reversal in Series Connection
SR batteries are primary cells with silver oxide as the positive electrode and zinc as the negative electrode, operating at approximately 1.55 V. They use an aqueous alkaline electrolyte (such as potassium hydroxide) and are not equipped with protective circuits like those found in rechargeable batteries.
When multiple button batteries are connected in series, continued discharge may cause the voltage of one cell to drop significantly, approaching zero. If discharge continues under these conditions, a phenomenon called polarity reversal occurs. During reversal, internal electrochemical reactions generate gas within the cell, causing a sharp rise in internal pressure. In sealed batteries, this pressure can cause the battery to bulge and ultimately lead to electrolyte leakage or rupture, posing a serious safety hazard.
This phenomenon can occur under conditions such as heavy-load discharge, mixing batteries of different capacities (including new and used cells), mixing batteries from different manufacturers, or using short-circuited cells. The same risks exist for LR button batteries, which also use an alkaline aqueous electrolyte.
3. Ensuring Safety and Maximizing Performance
A series connection of button batteries requires specific circuit design and safety considerations. Polarity reversal typically occurs at the end of discharge, but because it leads to hazardous conditions such as gas generation and pressure buildup, it must be prevented through proper device design.
- Conduct a safety assessment at the design stage that includes batteries.
- Include highly reliable batteries in packaging.
- Implement an over-discharge prevention mechanism.
- Avoid using three or more batteries in series.
- Ensure batteries are not short-circuited during installation.
For safety assurance, we strongly recommend consulting us during the early design phase. Depending on your design conditions, adjustments may be necessary, so early technical consultation is highly advisable.
Proper safety design, including battery considerations, is essential for ensuring reliability. In medical and precision devices, where safety and functionality must coexist, please make full use of our technical support.
Note: This document provides general guidelines for safe usage and does not constitute any warranty. Actual implementation conditions and safety must be verified against your own design standards, and prior consultation with us is required.
Glossary
Polarity Reversal: When multiple batteries are connected in series and discharge continues after a low-capacity cell is fully depleted, current still flows due to remaining capacity in other cells. The voltage of the depleted cell drops below zero, turning negative. This phenomenon is called polarity reversal.
