ZDNET’s key takeaways
- The risk is stored energy, not lithium metal.
- Bending and piercing cards made them warm, not hot – no smoke or flames.
- Stick with name brands and avoid no-name finder cards.
We’re told to be careful with lithium batteries. We’re told not to bend, flex, or crush them for fear of unleashing fiery death or disfigurement.
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On the other hand, tiny credit-card-style finder cards have become all the rage, and we slip these easily bendable, battery-containing gadgets into wallets and put them into back pockets, where we crush them with our buttocks on a daily basis.
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Does something feel wrong here?
Every time I write about them, someone asks me whether they’re dangerous. I must admit, it’s crossed my mind.
Tiny batteries, tiny risk
The batteries in a typical finder card are usually in the 110-400 mAh capacity range, with a nominal voltage of 3.7V. This can be either rechargeable or non-rechargeable, depending on the card type.
As a general rule of thumb — and it used to be a regulatory one — there’s about 0.3 g of lithium per Ah (or per 1,000 mAh). Using this, some back-of-the-envelope calculation shows that a 110 mAh cell contains 0.033 g of lithium (or 0.00116 oz), while a 400 mAh cell has 0.12 g (0.42329 oz) of the metal.
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Expressing these quantities in a way we can all visualize, the lithium in a 110 mAh cell is about the size of a single grain of short-grain rice, while the lithium in the bigger 400 mAh cell is about the size of a pea.
But — (there’s always a but, isn’t there? — this lithium isn’t rattling around inside a cell loose. No, instead it’s locked up in the battery in oxides, graphite, and electrolyte salts. The only metallic lithium in a cell is a tiny amount that gets plated on the anode (the internal positive pole of the battery) over time, or when the battery is charged in the cold, or when overcharged. And the amount plated is a fraction of the total lithium in the cell.
This means the lithium itself isn’t the issue. It’s the charge that the cell holds. When that charge is released unexpectedly — such as the cell being bent, causing an internal short circuit — it can ignite the electrolyte inside the battery. This, in turn, is what causes batteries in thermal runaway to flare and vent.
So far, this is all talk. What we need is some action.
Personal experiences
First, some anecdotes.
I’ve been testing these finder cards since their release, and while my buttocks are still unscathed, I have had a few cards physically break, split open, and splinter from being carried in a wallet (in my day-to-day, I use a ridged Ridge wallet, but I’ve got an old leather wallet that I use for testing this exact sort of thing).
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Beyond breaking apart, and leaving sharp shards in my pocket, nothing happened.
No fires. No flames or venting.
Also, as part of my testing, I’ve deliberately tried breaking apart cards, and let me tell you that there are some robust cards out there. Some you can break apart with effort; others I’ve only been able to damage. Sure, I could take shears, a grinder, or a sledgehammer to them and destroy them, but that’s way beyond what a finder card is going to experience during its life.
OK, so what about third-party anecdotes?
Not much. I found some reviews of a cheap, no-name card where one reviewer said the card swelled up when left in a car, and another who said that while charging the card, it “got really hot and melted a ballpoint pen nib size hole (.7mm) near the top and stopped working.”
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The only other thing I came across related to finder cards was a recall of an Anker product because its charging magnets could damage magnetic stripe cards. This was nothing related to safety.
The scarcity of anecdotes left me with one option: I could try to make some cards explode myself.
How to cause maximum damage
Before I go on, some words of caution — DON’T TRY THIS AT HOME (OR AT WORK)! I’ve got decades of experience handling batteries and electricity, and dealing with both when things go wrong.
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I took two new-ish cards (less than a couple of months old), both rechargeable, one from KeySmart, the other from Chipolo. They were both subjected to extreme abuse. I bent, twisted, and flexed them, focusing on the battery area to cause maximum damage.
Adrian Kingsley-Hughes/ZDNET
That didn’t seem to do much, so I upped my game and pierced the batteries multiple times with a metal blade.
Adrian Kingsley-Hughes/ZDNETThe best I got was that the batteries got a little warm. Warm, not even toasty.
While that’s not exciting, it’s what I expected from such a small battery.
Adrian Kingsley-Hughes/ZDNETThe bottom line
OK, so what’s my conclusion from all this?
Overall, finder cards are quite safe. The size and energy capacity of the batteries are such that even if they are critically damaged, they don’t produce flames or smoke.
Bear in mind that this is a small test of two cards, but the absence of tales of woe relating to these cards is also reassuring.
My advice is that these cards are safe, but to stick to name brands — Nomad, Chipolo, Rolling Square, Spotminders, Ugreen, and KeySmart are brands that I recommend — and avoid the cheap no-name stuff.
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If you’re still using an old-school leather wallet, you might want to go for one of the tougher finder cards out there. I found out for myself earlier this year just how tough these cards are, and how hard it is to get into them, even using extreme force.
I moved to rigid wallets a long time ago, recently swapping my Trayvax for a Ridge, and these are perfect for finder cards because they’re solid and do a very good job of resisting bending and flexing. And if you’d rather use an AirTag (I have to admit that Apple’s Precision Finding feature is useful), you can get a holder for that.
Either way, having a finder tag in your wallet or purse is a good way to reduce the frustration of misplacing or losing your cards and cash.
