It’s no exaggeration to say that the development of cheap rechargeable lithium-ion batteries has changed the world. Enabling everything from smartphones to electric cars, their ability to pack an incredible amount of energy into a lightweight package has been absolutely transformative over the last several decades. But like all technologies, there are downsides to consider — specifically, the need for careful monitoring during charging and discharging.

As hardware hackers, we naturally want to harness this technology for our own purposes. But many are uncomfortable about dealing with these high-powered batteries, especially when they’ve been salvaged or come from some otherwise questionable origin. Which is precisely what the Smart Multipurpose Battery Tester from [Open Green Energy] is hoping to address.

Based on community feedback, this latest version of the tester focuses primarily on the convenient 18650 cell — these are easily sourced from old battery packs, and the first step in reusing them in your own projects is determining how much life they still have left. By charging the battery up to the target voltage and then discharging it down to safe minimum, the tester is able to calculate its capacity.

It can also measure the cell’s internal resistance (IR), which can be a useful metric to compare cell health. Generally speaking, the lower the IR, the better condition the battery is likely to be in. That said, there’s really no magic number you’re looking for — a cell with a high IR could still do useful work in a less demanding application, such as powering a remote sensor.

If you’re not using 18650s, don’t worry. There’s a JST connector on the side of the device where you can connect other types of cells, such as the common “pouch” style batteries.

The open source hardware (OSHW) device is controlled by the Seeed Studio XIAO ESP32S3, which has been combined with the LP4060 charger IC and a AP6685 for battery protection. The user interface is implemented on the common 0.96 inch 128X64 OLED, with three buttons for navigation. The documentation and circuit schematics are particularly nice, and even if you’re not looking to build one of these testers yourself, there’s a good chance you could lift the circuit for a particular sub-system for your own purposes.

Of course, testing and charging these cells is only part of the solution. If you want to safely use lithium-ion batteries in your own home-built devices, there’s a few things you’ll need to learn about. Luckily, [Arya Voronova] has been working on a series of posts that covers how hackers can put this incredible technology to work.

When we saw [Max.K]’s automatic NiMh battery charger float past in the Hackaday tips line, it brought to mind a charger that might be automatic in the sense that any modern microcontroller based circuit would be; one which handles all the voltages and currents automatically. The reality is far cooler than that, a single-cell charger in which the automatic part comes in taking empty cells one by one from a hopper on its top surface and depositing them charged in a bin at the bottom.

Inside the case is a PCB with an RP2040 that controls the whole shop as well as the charger circuitry. A motorised cam with a battery shaped insert picks up a cell from the bin and moves it into the charger contacts, before dumping it into the bin when charged. What impresses us it how slick this device is, it feels like a product rather than a project, and really delivers on the promise of 3D printing. We’d want one on our bench, and after watching the video below the break, we think you will too.