Lithium-Ion Batteries: WHY They Demand Respect
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.
Three Thousand Participants
A 18650 cell is like a bigger sister to an AA battery – power at your fingertips, just, you’re playing with heaps more power. You can take a 18650 cell and have it power a small yet nimble robot on wheels, or an ultra powerful flashlight, or a handheld radio packing quite a transmit power punch. You can release its power on accident, too, and that gets nasty quick.
Short-circuiting a 18650 cell is a surprisingly straightforward way to melt metal, and by extent, start a small fire. It’s also not that hard to short-circuit a 18650 cell, especially and specifically unprotected ones. This is a big part of why consumer oriented gadgets use AAs instead of 18650s – it’s perhaps less powerful, sure, but it’s also a significantly less dangerous cell.
The Instructions, They Do Nothing!
WHY sold a little over 3700 tickets. I would not expect 100% attendance, but I’m comfortable saying it must’ve been around three thousand people. Sadly, “three thousand people” is far beyond the point when you can hope to give people handling instructions for something as easy to mishandle as LiIon cells, even for a nominally hacker audience.
Of course, you can try and give people instructions. You can talk to each badge recipient individually, release booklets demonstrating what to do and not to do with a 18650 cell, add silkscreen instructions for a just-in-place reminder, or maybe have them sign a release form, though it’s unlikely that kind of trick would be legal in the EU. Sadly, WHY organizers never came close to doing any of these things. It also wouldn’t really matter if they did. These instructions will always, inevitably be outright ignored by a sizeable percentage of users.
You can build a badge or any sort of other device using unprotected 18650s, which expects the end user to handle them, like the WHY badge does, and it will be more or less safe as long as the end user is yourself, with 18650 handling experience that I’m sure is to match. Giving it to a friend, caseless? You can talk to your friend and explain 18650 handling basics to them, sure, but you’re still running some degree of risk. My hunch is, your friend could very well refuse such a gift outright. Giving it to a hundred people? You’re essentially playing with fire at someone else’s house.
Just Why Did That Happen?
Hackaday has traditionally used AA cells for our badges, which has definitely help us mostly avoid any Lithium-related issues. Most other conferences have been using pouch cells, which traditionally come with short-circuit protection and don’t threaten to ignite stuff from contact with a piece of metal. 18650 cells are not even cheaper at scale – they’re nice, sure, I wrote as much, but those nice things are quickly negated by the whole “firestarter” thing.
On the other hand, 18650 cells do work for a hacker or a small team of hackers skilled enough to stay cautious, and it also works well at scale when the cell is permanently encased within the shell, like in most powerbanks and laptops. It fails as soon as you expect people to plug batteries in and out, or carry them separately. Respecting Lithium-Ion batteries means being aware of their shortcomings, and for 18650 cells, that means you should avoid having people manually handle them at scale.
Here’s the kicker about the WHY badge situation. I was confused by the WHY badge switching to 18650 cells this year, away from overcurrent-protected pouch cells, which were used by previous iterations of WHY (MCH, SHA) without an issue in sight. So, I’ve asked around, and what I got from multiple sources is – the 18650 usage decision was pushed top-down, with little regard for physical safety. Sadly, this makes sense – it’s how we saw it implemented, too.