Charge NiMH Batteries With Style, Panache And An RP2040

November 19, 2025 by Tyler August 20 Comments

The increasing dominance of lithium cells in the market place leave our trusty NiMH cells in a rough spot. Sure, you can still get a chargers for the AAs in your life, but it’s old tech and not particularly stylish. That’s where [Maximilian Kern] comes in, whose SPINC project was recently featured in IEEE Spectrum— so you know it has to be good.

With the high-resolution LCD, the styling of this device reminds us a little bit of the Pi-Mac-Nano— and anything that makes you think of a classic Macintosh gets automatic style points. There’s something reminiscent of an ammunition clip in the way batteries are fed into the top and let out the bottom of the machine.

[Maximilian] thought of the, ah, less-detail-oriented amongst us with this one, as the dedicated charging IC he chose (why reinvent the wheel?) is connected to an H-bridge to allow the charger to be agnostic as to orientation. That’s a nice touch. An internal servo grabs each battery in turn to stick into the charging circuit, and deposits it into the bottom of the device once it is charged. The LCD screen lets you monitor the status of the battery as it charges, while doubling as a handy desk clock (that’s where the RP2040 comes in). It is, of course powered by a USB-C port as all things are these days, but [Maximilian] is just drawing from the 5V line instead of making proper use of USB-C Power Delivery. (An earlier draft of this article asserted incorrectly that the device used USB-C-PD.) Fast-charging upto 1A is enabled, but you might want to go slower to keep your cells lasting as long as possible. Firmware, gerbers and STLs are available on GitHub under a GPL-3.0 license– so if you’re still using NiCads or want to bring this design into the glorious lithium future, you can consider yourself welcome to.

We recently featured a AA rundown, and for now, it looks like NiMH is still the best bang for your buck, which means this project will remain relevant for a few years yet. Of course, we didn’t expect the IEEE to steer us wrong.

Thanks to [George Graves] for the tip.

Teardown Of A Cheapish EBL Multi-Cell NiMH Charger

September 6, 2025 by Maya Posch 15 Comments

Bottom of the PCB with most of the ICs. (Credit: Brian Dipert, EDN)

People think about NiMH cell chargers probably as much as they think about batteries, unless it’s time to replace the cells in whatever device they’re installed in. This doesn’t make a teardown of one of these marvels any less interesting, especially when you can get an 8-bay charger with eight included NiMH cells for a cool $25 brand new. The charger even has USB ports on it, so it’s got to be good. Cue a full teardown by [Brian Dipert] over at EDN to see what lurks inside.

Of note is that [Brian] got the older version of EBL’s charger, which requires that two cells of the same type are installed side-by-side instead of featuring per-bay charging. This is a common feature of cheaper chargers, and perhaps unsurprisingly the charger was struggling with NiMH cells that other chargers would happily charge.

Opening up the unit required hunting for plastic clips, revealing the rather sparse internals. Unsurprisingly, there wasn’t a lot to look at, with the two USB ports apparently wired directly into the AC-to-DC section. There’s a CRE6536 AC-DC power management IC, the full-bridge rectifier and an unmarked 16-pin IC that presumably contains all of the charger logic. On the positive side, the mains-powered charger didn’t catch on fire (yet), but for anyone interested in leaving battery chargers unattended for extended periods of time, perhaps look at a more reputable brand.

Handheld 18650 Analyzer Scopes Out Salvaged Cells

April 3, 2025 by Tom Nardi 11 Comments

You can salvage lithium 18650 cells from all sorts of modern gadgets, from disposable vapes to cordless power tools. The tricky part, other than physically liberating them from whatever they are installed in, is figuring out if they’re worth keeping or not. Just because an 18650 cell takes a charge doesn’t necessarily mean it’s any good — it could have vastly reduced capacity, or fail under heavy load.

If you’re going to take salvaging these cells seriously, you should really invest in a charger that is capable of running some capacity tests against the cell. Or if you’re a bit more adventurous, you can build this “Battery Health Monitor” designed by [DIY GUY Chris]. Although the fact that it can only accept a single cell at a time is certainly a limitation if you’ve got a lot of batteries to go though, the fact that it’s portable and only needs a USB-C connection for power means you can take it with you on your salvaging adventures.

The key to this project is a pair of chips from Texas Instruments. The BQ27441 is a “Fuel Gauge” IC, and is able to determine an 18650’s current capacity, which can be compared to the cell’s original design capacity to come up with an estimate of its overall health. The other chip, the BQ24075, keeps an eye on all the charging parameters to make sure the cell is being topped up safely and efficiently.

With these two purpose-built chips doing a lot of the heavy lifting, it only takes a relatively simple microcontroller to tie them together and provide user feedback. In this case [DIY GUY Chris] has gone with the ATmega328P, with a pair of addressable WS2812B LED bars to show the battery’s health and charge levels. As an added bonus, if you plug the device into your computer, it will output charging statistics over the serial port.

The whole project is released under the MIT license, and everything from the STL files for the 3D printed enclosure to the MCU’s Arduino-flavored firmware is provided. If you’re looking to build one yourself, you can either follow along with the step-by-step assembly instructions, or watch the build video below. Or really treat yourself and do both — you deserve it.

If your battery salvaging operation is too large for a single-cell tester, perhaps it’s time to upgrade to this 40-slot wall mounted unit.

Continue reading “Handheld 18650 Analyzer Scopes Out Salvaged Cells” →

Playing Around With The MH-CD42 Charger Board

December 27, 2024 by Tom Nardi 12 Comments

If you’ve ever worked with adding lithium-ion batteries to one of your projects, you’ve likely spent some quality time with a TP4056. Whether you implemented the circuit yourself, or took the easy way out and picked up one of the dirt cheap modules available online, the battery management IC is simple to work with and gets the job done.

But there’s always room for improvement. In a recent video, [Det] and [Rich] from Learn Electronics Repair go over using a more modern battery management board that’s sold online as the MH-CD42. This board, which is generally based on a clone of the IP5306, seems intended for USB battery banks — but as it so happens, plenty of projects that makers and hardware hackers work on have very similar requirements.

So not only will the MH-CD42 charge your lithium-ion cells when given a nominal USB input voltage (4.5 – 5 VDC), it will also provide essential protections for the battery. That means looking out for short circuits, over-charge, and over-discharge conditions. It can charge at up to 2 A (up from 1 A on the TP4056), and includes a handy LED “battery gauge” on the board. But perhaps best of all for our purposes, it includes the necessary circuitry to boost the output from the battery up to 5 V.

If there’s a downside to this board, it’s that it has an automatic cut-off for when it thinks you’ve finished using it; a feature inherited from its USB battery bank origins. In practice, that means this board might not be the right choice for projects that aren’t drawing more than a hundred milliamps or so.

Continue reading “Playing Around With The MH-CD42 Charger Board” →

OSHW Battery Tester Aims To Help Tame Lithium Cells

December 3, 2024 by Tom Nardi 13 Comments

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.

Continue reading “OSHW Battery Tester Aims To Help Tame Lithium Cells” →

The Automatic Battery Charger You Never Knew You Needed

December 2, 2024 by Jenny List 47 Comments

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 motorized 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.

Continue reading “The Automatic Battery Charger You Never Knew You Needed” →

Change The Jingle In Your Makita Charger Because You Can

February 16, 2024 by Lewin Day 20 Comments

Lots of things beep these days. Washing machines, microwaves, fridge — even drill battery chargers. If you’re on Team Makita, it turns out you can actually change the melody of your charger’s beep, thanks to a project from [Real-Time-Kodi].

The hack is for the Makita DR18RC charger, and the implementation of the hack is kind of amusing. [Real-Time-Kodi] starts by cutting the trace to the buzzer inside the charger. Then, an Arduino is installed inside the charger, hooked up to the buzzer itself and the original line that was controlling it. When it detects the charger trying to activate the buzzer, it uses this as a trigger to play its own melody on the charger instead. The Arduino also monitors the LEDs on the charger in order to determine the current charge state, and play the appropriate jingle for the situation.

It’s an amusing hack, and one that could certainly confuse the heck out of anyone expecting the regular tones out of their Makita charger. It also shows that the simple ways work, too — there was no need to dump any firmware or decompile any code.

Continue reading “Change The Jingle In Your Makita Charger Because You Can” →