Lithium-Ion Batteries: WHY They Demand Respect

November 4, 2025 by Arya Voronova 48 Comments

This summer, we saw the WHY (What Hackers Yearn) event happen in Netherlands, of course, with a badge to match. Many badges these days embrace the QWERTY computer aesthetic, which I’m personally genuinely happy about. This one used 18650 batteries for power, in a dual parallel cell configuration… Oh snap, that’s my favourite LiIon cell in my favourite configuration, too! Surely, nothing bad could happen?

Whoops. That one almost caught me by surprise, I have to shamefully admit. I just genuinely love 18650 cells, in all glory they bring to hardware hacking, and my excitement must’ve blindsided me. They’re the closest possible entity to a “LiIon battery module”, surprisingly easy to find in most corners of this planet, cheap to acquire in large quantities, easy to interface to your projects, and packing a huge amount of power. It’s a perfect cell for many applications I and many other hackers hold dear.

Sadly, the 18650 cells were a bad choice for the WHY badge, for multiple reasons at once. If you’re considering building a 18650-based project, or even a product, let me show you what exactly made these cells a bad fit, and how you might be able to work around those limitations on your own journey. There’s plenty of technical factors, but I will tell you about the social factors, because these create the real dealbreaker here. Continue reading “Lithium-Ion Batteries: WHY They Demand Respect” →

The WHY 2025 Badge And Its 18650s

August 12, 2025 by Jenny List 38 Comments

The largest European hacker camp this year was in the Netherlands — What Hackers Yearn (WHY) 2025 is the latest in the long-running series of four-yearly events from that country, and 2025 saw a move from the Flevoland site used by SHA2017 and MCH2021, back to just north of Alkmaar in Noord-Holland, where the OHM2013 event took place. WHY has found itself making the news in the Dutch technical media for all the wrong reasons over the last few days, after serious concerns were raised about the fire safety of its badge.

The cell supplied with a WHY 2025 badge, with very clear fire safety warning — This is the cell supplied with the WHY badge, complete with manufacturer’s warning.

The concerns were raised from the RevSpace hackerspace in Leidschendam, and centre around the design of the battery power traces on the PCB between the battery holders and the power supply circuitry. Because the 18650 cells supplied with that badge lack any protection circuitry, bridging the power traces could be a fire risk.

In short: their report names the cell holders as having tags too large for their pads on the PCB, a too-tight gap between positive and negative battery traces, protected only by soldermask, and the inadequacy of the badge’s short circuit protection. In the event that metal shorted these battery tags, or wore through the soldermask, the batteries would be effectively shorted, and traces or components could get dangerously hot.

The WHY organizers have responded with a printed disclaimer leaflet warning against misuse of the cells, and added a last-minute epoxy coating to the boards to offer additional protection. Some people are 3D-printing cases, which should also help reduce the risk of short-circuiting due to foreign metal objects. Using an external powerbank with short-circuit protection instead of the cells would solve the problem as well. Meanwhile a group of hackers collecting aid for Ukraine are accepting the batteries as donations.

It’s understood that sometimes bugs find their way into any project, and in that an event badge is no exception. In this particular case, the original Dutch badge team resigned en masse at the start of the year following a disagreement with the WHY2025 organizers, so this badge has been a particularly hurried production. Either way, we are fortunate that the issue was spotted, and conference organizers took action before any regrettable incidents occurred.

The Negative Rail Explained

November 9, 2018 by Tom Nardi 45 Comments

With the high availability of modular components and incredible wealth of information and tutorials online, it’s now easier than ever for hackers and makers to assemble complex electronic projects without getting bogged down with the theory behind it all. But the downside is that the modern electronic hobbyist often doesn’t have as deep an understanding of the low-level concepts that they would have if they had to build everything from scratch. This can be a problem when they try diagnosing and repairing faults, or when they start to branch out into reverse engineering.

Which makes “Building Blocks” by [David Christensen] a very compelling series. Every week he will be demonstrating a new circuit on his blog, complete with a plain English explanation of how and why it’s used. In this first installment of the series, he’s tackling a concept most of us have seen when poking around in more complex electronic devices, but maybe never really gave much thought to: the negative rail.

What exactly is the negative rail, anyway? It’s pretty easy to understand the positive rail in a circuit and its relation to ground; even multiple positive rails, such as in devices which use both 5 V and 3.3 V, are simple enough to wrap your head around. Unfortunately when something drops below that logical 0V reference, it isn’t quite as intuitive. But as [David] explains, the negative rail in a circuit is critical for dealing with bipolar signals, such as audio, which ride above and below the 0 V center point.

[David] goes over a few methods used to create the negative rail, from the classic center-tap transformer to using a buck-boost converter. But not content with just describing how these circuits work, he walks the reader through the creation of a charge pump circuit that you can drop into your next project if you find yourself in need of the elusive voltage. After explaining and diagramming it, he builds the circuit on a scrap piece of copper clad board and puts it through some benchmarks to prove it matches the theory he laid out.

If you’re in the mood for more negative talk, check out the battle our very own [Steven Dufresne] had with voltages of varying polarity when building his BB-8 robot.