DIY Guy Chris Builds a Flexible Battery Charger That Provides At-a-Glance Health Information
Open-hardware design can charge and test a variety of battery types — and can even act as a powerbank itself.
Mohamed Belkhir, also known as "DIY Guy Chris," has designed a slick-looking battery monitor designed to track state of charge and state of health of a range of battery types — providing at-a-glance LED bar charts for both metrics.
"Just because a battery charges properly doesn't necessarily mean it's in a good health," Chris advises in the introduction to his latest video. "Knowing the state of health of a battery is crucial for ensuring the reliability of your devices and appliances — but how do you measure the state of health?"
In Chris' case, the answer is simple: by building a device for doing exactly that. Typically, a battery tester works by reading the voltage coming out of the battery: if it's high, it's a sign the battery is good; if it's low, the battery is on its way out if it's a disposable or needs charging if it's a rechargeable. This is "state of charge" — but Chris is interested in a second, more complex metric: "state of health."
"State of health refers to the overall condition and capacity of a battery compared to when it was brand new," Chris explains. "It reflects how much the battery has aged or degraded over time and tells you how effectively it can store and deliver energy."
To gather both state of charge and state of health metrics, Chris designed a portable tool which is built around a Microchip ATmega328P microcontroller connected to a Texas Instruments BQ27441 fuel gauge chip and a BQ24075 battery charging chip. The board, housed in a neat 3D-printed case, accepts a range of battery types — 18650 cells, external batteries with a JST connector, or ones connected through screw terminals — and charges them from a USB Type-C power supply, updating LED bar graphs showing the battery health and charge levels in real-time.
"Additionally you can receive precise data from this device through the serial port," Chris adds, "and display it on any serial monitor with the Arduino Serial Monitor being a great tool for this purpose. The device provides a regulated output, allowing you to not only charge a battery but also power other devices through the JST connector."
The project is documented in detail in the video embedded above and on Chris' YouTube channel; design files, Gerbers, a bill of materials, pick-and-place file, firmware code, and 3D print files for the case are available on GitHub under the permissive MIT license.
