Testing LFP Battery Failure Modes With Overcharging

May 28, 2026 by Maya Posch 33 Comments

As great as batteries are, it’s essential to understand their risks and how to keep them from going spicy. Recently there has been a bit of a fuss about the dangers of LiFePO₄ (LFP) batteries after someone’s dedicated LFP battery shed got shredded into matchsticks by a hydrogen explosion, following said LFP batteries having a thermal event. The thing about the LFP chemistry is that if it suffers such a thermal event, it generates hydrogen gas, which is one of the most explosion-happy gases known to man. This is demonstrated in a recent video by [Will Prowse].

To kick things off, a single prismatic LFP cell is overcharged for half an hour after it was already at 100% state of charge. This ultimately pops the vent as the cell begins to release hydrogen gas into the aquarium that the cell was placed in. Using a spark generator it’s then attempted to ignite the gas, which initially takes a bit as enough hydrogen has to collect first.

Once there’s ignition, however, it happily keeps burning as more and more hydrogen pours out of the by now bulging cell’s vent. If any other LFP cells had been nearby these too would be at risk of suffering thermal runaway, showing how just one bad LFP cell is enough to potentially set an LFP battery bank ablaze.

In a commercial setting you will have precautions such as hydrogen sensors, ventilation and spark generators to deal with any generated hydrogen gas, as well as blow-out panels in case things end up going squirrely in a hurry.

While a benefit of LFP chemistry is that it does not generate its own oxygen as with other lithium-ion chemistries, hydrogen gas is a major problem due to how incredibly volatile it is. It’s not just a headache with battery storage, but also in the nuclear power sector, where zirconium fuel rod cladding can very efficiently turn steam into hydrogen and oxygen. This was the reason why some of Fukushima Daiichi’s buildings suffered detonations, with the nuclear plant operator opting to not install recommended hydrogen gas mitigation systems.

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A ZInc Air Battery You Can Make Yourself

May 26, 2026 by Jenny List 9 Comments

Zinc air batteries have been a familiar sight for decades in the world of photography, where they provided an environmentally less dangerous alternative to mercury cells. They operate by the oxidation of metallic zinc using air, and the zinc comes in the form of a paste spread between two electrodes. Can their astounding energy density be harnessed for something useful? [ZollerLab] has designed a zinc air battery to find out, and is using it to power a rudimentary model car.

The video below is in German so you’ll have to enable translated subtitles if you’re an Anglophone, and it’s very long. But it goes into extreme detail on the chemistry, construction, and constraints of a zinc-air battery, and describes the system in this design. It’s a stack arrangement, in which the cells are held together on threaded rods, and pushed into each other with springs.

We think the car model is intended to demonstrate that this battery chemistry might one day be used in automotive applications. It’s not such a far-fetched idea given the low cost, relatively low environmental footprint, and high energy density, indeed we’ve heard of similar experiments with aluminium primary cells. But in this case we can see it provides the hacker with another route for their experiments, and that’s no bad thing.

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ChargeCap Helps Your Batteries Last Longer By Limiting Charge Level

May 14, 2026 by Donald Papp 22 Comments

If you want to maximize the life of your lithium-ion batteries, proper storage voltage is critical. That is, don’t store them empty, and don’t store them completely full either. “Almost fully charged” is a sweet spot for occasional-use devices. Sadly, this is easier said than done. While many devices use integrated rechargeable batteries these days, most provide no method of limiting charge level. That’s where [DaverDavid]’s ChargeCap comes in.

By sampling charge current and disconnecting when it drops to 50 percent of peak, charging is reliably stopped when the target device is 80 to 90 percent charged, regardless of cell count or capacity.

ChargeCap sits between a USB charger and target device, disconnecting when it detects that recharging is 80 to 90 percent complete. This is particularly useful for maximizing the cell life of devices that see only intermittent use.

The way ChargeCap does this is clever, and relies on the fact that all lithium-ion charging curves look the same regardless of cell capacity or cell count. Charge current remains at pretty much the same level for most of the charging process, but tapers off quickly (and in a linear fashion) as cells approach their maximum capacity. That’s because charging a battery is a lot like blowing up a balloon: the first breaths are easy, but once the balloon fills out, every breath needs to push harder than the last.

ChargeCap works by sampling the peak charge current at the beginning of the charge cycle, then detecting when it drops below 50 percent of peak, at which point charging is stopped. The result is a device that reliably charges to 80 to 90 percent of capacity, and no more. ChargeCap uses an ESP32-C3 and a small OLED display that, as a nice touch, inverts colors to signal charge completion. Design files and code are at the GitHub repository.

Lithium-ion cells are fantastic devices, so flesh out your knowledge by reading [Arya Voronova]’s primer on designing them into your own projects, or a more in-depth explanation of how they work.

Teardown: ChargeTab Emergency Phone Charger

May 14, 2026 by Tom Nardi 58 Comments

If you own a modern smartphone, there’s an excellent chance that its battery has run dangerously low on you at least a few times. Murphy’s Law dictates that this will naturally occur at the worst possible moment, say when you need to make an important phone call or when you’re lost and need to navigate home.

With this in mind, it’s not hard to see how a product like the ChargeTab would have a certain appeal. A small $10 USD device that you can keep in the car or pack in a bag that’s always available to charge your phone in an emergency.

Because it’s not meant to be used regularly — indeed it may never get used at all — it’s not completely unreasonable that such a device would only be good for one or two charges before its spent and must be replaced. It’s a bit like keeping a road flare in the car; it’s unlikely you’ll ever use the thing, but if you do, it only needs to work once.

But then what? According to ChargeTab, once the gadget has depleted its internal ~3,000 mAh battery it cannot be recharged and is no longer usable. Now to be fair, they specifically tell you to not throw it in the trash. They’ll send you a free return label to ship it back to them, at which point it will be refurbished and put back into circulation. The company argues that this recycling program, combined with the fact that the batteries inside the ChargeTabs were supposedly diverted from landfills in the first place, makes their entire operation eco-friendly.

Yet here we have a pair of ChargeTabs that were thrown in the regular garbage and would have taken a one-way trip to the local landfill if it wasn’t for the fact that I habitually dig through garbage cans like a raccoon. So let’s take a look at what’s inside one of these emergency phone chargers and if the idea is as green as the company claims.

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Electric Wind-Up Plane Uses Supercapacitors For Free Flight Fun

April 18, 2026 by Tyler August 21 Comments

There’s something to be said for a simple wind-up, free flight model airplane. With no controls, it must be built very well to fly well, and with only the limited power of a rubber band, it needs a good, high-lift design without much superfluous drag to maximize flight time. There’s also something to be said for modernity though, and prolific hacker [Tom Stanton] puts them together with this supercapacitor plane.

If that sounds familiar, it’s because [Tom] did this before back in 2023. But for that first attempt he converted a commercial R/C toy rather than a plane optimized for low-power free flight. Just like with the best rubber-band machines, his goal for the new production is more flight time than winding time. Plus lots of views on YouTube, but that goes without saying.

Thus this machine is smaller and lighter than the previous iteration. Rather than balsa and tissue like the free-flight aircraft of our youths, [Tom] is using 3D printed plastic for the structure. But he’s got a neat hack built in: he’s printing the wings and control surfaces directly onto tissue paper, eliminating the bonding step. Of course that means his wings are printed flat, but a bit of heat and some bending and he has a single-surface airfoil. Single-surface airfoils are normal in this application, anyway: closed wings add too much weight for too little gain. If you want to try the technique, he’s got files on Printables.

Another interesting factoid [Tom] discovered is that the energy density of supercapacitors decreases sharply below 10 F. As you might imagine by the square-cubed law, bigger is better, but the sharp drop-off dictated he use a single 10 F cap for this build, along with a micro motor. Using the wind-up generator from his previous build, he’s able to get 45 seconds of flight out of just 4 seconds of cranking, a good ratio indeed.

[Tom] seems to like playing with different ways to power his toys; aside from supercapacitors, we’ve also seen him finessing aircraft air motors — including an attempt at a turbine for a model helicopter.

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Battle Born Explains How Its Battery Thermal Safety Works

April 10, 2026 by Maya Posch 65 Comments

Autopsy of Battle Born LFP battery with the 'thermal safety' on the bus bar. (Credit: Will Prowse) — Autopsy of Battle Born LFP battery with the ‘thermal safety’ on the bus bar. (Credit: Will Prowse)

After users of Battle Born LFP batteries encountered issues such as a heavily discolored positive terminal and other signs of overheating, multiple autopsies showed that the cause appeared to be the insertion of a thermoplastic between the bus bar and the terminal. Over time thermal creep loosened the connections, causing poor contact and melting plastic enclosures. According to Battle Born, this is actually part of an ingenious thermal safety design, and in a recently published article they explain how it works.

The basic theory appears to be that if there’s a thermal event, the ABS thermoplastic will soften and reduce the pressure on the bolted-together copper bus bar and brass terminal. This then allows for an aluminium-oxide layer to form on the aluminium connecting bolt courtesy of the dissimilar copper/aluminium interface. Aluminium-oxide is non-conductive and thus interrupts the flow of current.

Of course, there are countless issues with that theory, least of all the many reports of in-field failures. We recently covered [Will Prowse] studying the death of one of these 100 Ah LFP batteries from brand-new to failure under controlled circumstances. This clearly shows the thermal creep loosening up the connection and causing poor contact between the bus bar, the bolt and the terminal, with poor contact and thermal issues resulting.

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Post-Failure Autopsy And Analysis Of An LFP Battery

April 2, 2026 by Maya Posch 8 Comments

Recently [Kerry Wong] had one of his Cyclenbatt LiFePO₄ batteries die after only a few dozen cycles, with a normal voltage still present on the terminals. One of the symptoms was that as soon as you try to charge it, the voltage goes up very rapidly to above 14 V due to what appears to be high internal resistance, and vice versa for discharging. In addition, the Bluetooth feature of the BMS appeared to have died as well, making non-invasive diagnostics somewhat tricky.

Close-up of the BMS. (Credit: Kerry Wong, YouTube)

After gently cutting open the plastic case, [Kerry] was greeted by the happily blinking blue LED of the Bluetooth module and deepening the mystery. Overall the build quality looks to be pretty good, with no loose cables as seen with certain other LFP batteries.

Cell voltages measured normal, with no significant imbalance. Next was measuring the internal resistance, which showed a clear issue. One of the cells was reading over 3 Ohms, whereas the others were in the milli-Ohm range. This would definitely explain the issues with charging and discharging, with a single bad cell causing most of the issues.

Of course, why the Bluetooth feature failed remains a mystery, and there’s still a lingering question on whether the BMS practiced proper balancing between the cells, as this can also cause issues over time.

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