Hey everyone, welcome back to My Weird Prompts. I am Corn, and I am here with my brother, the man who probably has a spreadsheet for every battery in this house.
Herman Poppleberry at your service. And you are not wrong, Corn. I actually checked the health of our laptop batteries just last Tuesday. It is a necessary habit.
Of course it is. Well, we have a really interesting one today. Our housemate Daniel sent us a voice note from the couch. He is still fighting off that cold, so he has had some time to do some deep thinking and some online shopping. He was looking for a heat gun for some do it yourself projects and noticed that AliExpress and other retailers have these really specific, almost confusing rules about shipping batteries.
It is a classic logistics puzzle. Daniel noticed that if the battery is loose or detachable, it is often a no go for international shipping, but if it is built into the device, it comes right through. And he also asked about how this works when we are actually flying, like why we can carry batteries in the cabin but not in our checked luggage.
It is one of those things we all just kind of accept as a rule of travel, like taking off your shoes at security, but the actual science and the regulatory logic behind it are pretty intense. I mean, we are talking about high energy density devices that can essentially become miniature blowtorches if things go wrong.
Exactly. And I love that Daniel brought this up because it touches on everything from chemical engineering to international maritime law and aviation safety. There is a whole world of hazard classifications that determine how these little power bricks move around the globe.
So let us start with the shipping side of things. Why does AliExpress or Amazon for that matter care so much if the battery is inside the tool or next to it in the box? To a normal person, it is the same amount of lithium, right?
You would think so, but from a regulatory standpoint, it changes everything. This comes down to the United Nations Committee of Experts on the Transport of Dangerous Goods. They have these specific numbers called UN numbers that classify materials. For lithium ion batteries, the big ones are UN thirty four eighty and UN thirty four eighty one.
Okay, break those down for me. What is the difference?
UN thirty four eighty is for lithium ion batteries shipped by themselves. Just the batteries. UN thirty four eighty one is for lithium ion batteries contained in equipment or packed with equipment. Now, the reason retailers like AliExpress struggle with the loose batteries, the UN thirty four eighty category, is that they are considered fully regulated Class Nine Dangerous Goods.
Class Nine. That sounds serious.
It is. When you ship loose batteries, the packaging requirements are much stricter. You need specialized boxes that have been drop tested, specific labeling, and the shipping costs skyrocket because many passenger planes will not carry them at all. They have to go on dedicated cargo aircraft. Also, as of the latest ICAO updates, loose batteries shipped as cargo must be at a state of charge of thirty percent or less. That is hard for a factory to manage and verify for every single unit.
So if I buy a heat gun and the battery is already clicked into the handle, or even just inside the casing, it falls under that other category, UN thirty four eighty one?
Precisely. When a battery is inside a device, the device itself acts as a protective shell. It prevents the battery from being crushed or punctured easily. But more importantly, it prevents the battery terminals from touching something metallic and short circuiting. If you have a bunch of loose batteries in a box and they shift during transit, and a positive terminal touches a negative terminal via a stray piece of metal or even another battery, you get a short. That leads to heat, which leads to thermal runaway.
Thermal runaway. That is the term everyone hears but maybe does not fully understand. What is actually happening inside the cell when that starts?
It is a feedback loop. Think of it as a chemical fire that provides its own fuel and its own oxygen. If a cell gets too hot, the separator between the anode and the cathode melts. Once that happens, all that stored energy is released at once as heat. That heat then causes the neighboring cells to fail, which releases more heat. It is a chain reaction that can reach temperatures over seven hundred degrees Celsius in seconds.
Seven hundred degrees. That is hot enough to melt aluminum.
Oh, easily. And the scary part is that a lithium ion fire produces its own oxygen through the breakdown of the cathode material. So you cannot just smother it like a normal fire. You can cut off the outside air, and it will just keep screaming along.
So when Daniel sees that the built in battery is okay to ship, it is because the engineers have essentially designed a safety cage around that potential fire. The device casing provides physical protection and ensures the terminals stay isolated.
Right. And there is another layer to this. For shipping, built in batteries often fall under what they call Section Two of the packing instructions. If the battery is under a certain capacity, like one hundred watt hours for a battery pack or twenty watt hours for a single cell, and it is inside a device, the regulations are much more relaxed. You do not need the full dangerous goods documentation or the expensive specialized handling. That is why AliExpress can ship you a phone or a laptop with no problem, but they will cancel your order for five loose eighteen six hundred fifty cells.
That makes a lot of sense. It is about the risk of a short circuit during the chaos of shipping and handling. But let us pivot to Daniel's other question, which is about flying. This is where it gets really counterintuitive for a lot of people. If I have a power bank, the airline insists it stays in my carry on. They absolutely do not want it in the cargo hold. But wait, isn't the cargo hold where the fire suppression systems are? Why would they want the fire in the cabin with the people?
This is one of the most fascinating parts of aviation safety logic. It sounds backwards, but it is actually a very calculated decision. There are two main reasons. The first is detection. If a battery starts to smoke in a carry on bag in the overhead bin, someone is going to smell it or see it almost immediately. The flight attendants are trained for this. They have specialized fire containment bags, which are basically heavy duty, high temperature sacks they can drop the device into.
So human eyes and noses are the best smoke detectors we have.
Exactly. Fast detection is key. The second reason is the type of fire. Like I mentioned, lithium fires are incredibly difficult to put out. In the cabin, the crew can use water or a non flammable liquid to cool the battery. While water is usually a bad idea for electrical fires, for a lithium ion battery in thermal runaway, the goal is actually to pull heat away from the neighboring cells to stop the chain reaction. You are essentially dousing it to keep it from spreading.
Okay, so if that same battery is in the cargo hold, what happens? There aren't any flight attendants down there with water bottles.
That is the problem. Most modern passenger planes use a fire suppression gas called Halon thirteen zero one in their cargo holds. Halon is amazing at putting out a suitcase that is on fire or a box of clothes. It works by chemically interrupting the combustion process. However, Halon does not work on lithium ion batteries.
Wait, it doesn't work at all?
It will put out the open flames, but because the battery is undergoing a chemical reaction that generates its own heat and oxygen internally, the Halon cannot stop the thermal runaway itself. The battery will keep cooking, and once the Halon concentration in the hold drops, the fire can just flare right back up.
That is terrifying. So you have a fire that the automated system cannot actually extinguish, and it is hidden under hundreds of suitcases where nobody can see it until it is potentially too late.
Precisely. In twenty thirteen, the Federal Aviation Administration did a series of tests where they put a bunch of lithium batteries in a simulated cargo hold and triggered a thermal runaway. They found that the Halon suppressed the fire, but the pressure from the gases released by the batteries actually blew the door off the cargo hold. The batteries release hydrogen and other flammable gases as they fail. If those gases build up and then find a spark, you get an explosion.
So the policy of keeping batteries in the cabin is basically saying, we would rather have a fire we can see and fight manually than a hidden fire that might blow a hole in the side of the plane.
That is exactly the trade off. It is about manageability. In the cabin, it is a manageable incident. In the hold, it is a potential catastrophe.
Now, Daniel mentioned his electric toothbrush. He said he usually packs that in his checked luggage. And a lot of people do that with electric shavers or toothbrushes. Is that actually a violation of the rules, or is there a loophole there?
It is generally allowed, but it is a bit of a gray area. Most airlines allow small devices with built in batteries in checked bags as long as they are completely turned off and protected from accidental activation. You do not want your toothbrush vibrating for eight hours and overheating. But even then, safety experts will tell you that the safest place for any lithium battery, no matter how small, is in the cabin.
So the rule is really about the loose batteries again. The power banks, the spare camera batteries, the loose cells for a flashlight. Those are the high risk items because they have exposed terminals and no outer protective casing from a tool or a device.
Right. If you have a spare battery and the terminals touch a coin or a zipper in your suitcase, that is your ignition source right there. That is why if you must carry spare batteries, the recommendation is always to put them in individual plastic bags or put tape over the terminals.
I want to go back to the cargo hold for a second. You mentioned Halon. I am curious about the actual tech down there. How does a plane even know there is a fire in the hold? It is not like there is a guy with a thermal camera watching the suitcases.
It is actually a very sophisticated system. Most cargo holds are what they call Class C compartments. To be a Class C hold, you need two things: a separate smoke detection system and a built in fire suppression system. The smoke detectors are usually optical. They use light scattering. Basically, a beam of light is sent across a sensor, and if smoke particles enter the chamber, they scatter the light onto a receiver, which triggers the alarm in the cockpit.
And once that alarm goes off, what does the pilot do? Do they just hit a big red button?
Pretty much. They have a switch that discharges the first bottle of Halon. This is called the high rate discharge. It floods the cargo hold immediately to knock down any flames. But here is the clever part: they also have a second bottle, or a series of bottles, called the low rate discharge. This slowly leaks Halon into the hold for the rest of the flight, sometimes for up to several hours, to keep the concentration high enough to prevent the fire from re igniting while the pilot looks for the nearest airport to land.
That is incredible. So it is not just one blast; it is a sustained chemical environment designed to keep the fire asleep until they can get on the ground.
Exactly. But again, that system was designed for burning luggage, not for lithium batteries. This is why the International Civil Aviation Organization actually banned the transport of lithium ion batteries as cargo on passenger planes back in twenty sixteen. If you see a big pallet of iPhones on a plane, that plane is almost certainly a dedicated cargo freighter, not the flight you are taking to visit your grandma.
That is a huge distinction. So the batteries we are carrying in our pockets are literally the only lithium batteries on the entire passenger plane, aside from what is built into the aircraft's own systems.
For the most part, yes. And even the aircraft's own batteries have been redesigned. Remember the Boeing seven eighty seven Dreamliner issues back in twenty thirteen? They had those battery fires that grounded the whole fleet. The fix was not just making the batteries better; it was encasing the entire battery in a heavy stainless steel box with a vent pipe that leads directly to the outside of the aircraft. So if the battery fails, the fire and the toxic gases are literally piped overboard.
Talk about a second order effect. You have to design a chimney for your battery just in case it decides to self destruct.
It is the only way to be sure.
So, looking forward, do you think these regulations are going to get even stricter? I mean, we are putting lithium batteries in everything now. I saw a heated jacket the other day that uses a massive power bank. People are wearing these things on planes.
It is a constant battle between energy density and safety. The more energy we cram into a small space, the more dangerous that space becomes. There is a lot of hope for solid state batteries. These would replace the flammable liquid electrolyte with a solid material that is much more stable. If we can get solid state batteries into the mainstream, a lot of these shipping and travel restrictions might actually vanish because the risk of thermal runaway would be almost zero.
That would be a game changer for logistics. Imagine AliExpress being able to ship whatever they want without worrying about the plane catching fire.
It would save billions in shipping costs. But until then, we are stuck with the rules. And honestly, the rules are there for a reason. I have seen videos of eighteen six hundred fifty cells failing, and it is not a fire you want to be near, especially at thirty five thousand feet.
You know, it occurs to me that there is a bit of a psychological gap here. We use these devices every day. I am holding a phone right now, you have a laptop on your lap. We trust them completely. But the moment they go into a cardboard box or a suitcase, they become Hazmat.
It is all about the environment. In your hand, you are monitoring the device. If your phone gets hot, you put it down. You notice if the screen starts to bulge because the battery is swelling. But in a shipping container at the bottom of a pile of ten thousand other boxes, there is no one to notice those early warning signs. Logistics is all about planning for the worst case scenario in an unmonitored environment.
That is a great way to put it. It is the transition from a monitored personal item to an unmonitored piece of cargo.
Precisely. And for our listeners, there is a practical takeaway here. If you are buying electronics from overseas, and you see that the shipping is unusually expensive or it says it has to go by sea, it is probably because of that UN thirty four eighty classification. It is not just the retailer being difficult; it is them following international law to make sure the plane stays in the air.
And if you are packing for a trip, take the extra two minutes to move your batteries to your carry on. Even the small ones. It is not just about following the rules; it is about giving the flight crew a fighting chance if something goes sideways.
And check your watt hours. Most airlines have a limit of one hundred watt hours for a single battery. You can sometimes bring larger ones, up to one hundred sixty watt hours, but you usually need prior approval from the airline. If you try to bring a massive professional cinema camera battery or a huge e bike battery, they might stop you at the gate.
One hundred watt hours. How do people find that number? It is usually not written in big letters on the side.
You have to do a little bit of math, which I know is everyone's favorite part of travel. Most batteries list milliamp hours and volts. To get watt hours, you multiply the amp hours by the nominal voltage. Now, here is the trick: most power banks use internal cells rated at three point seven volts. So a twenty thousand milliamp hour power bank is actually seventy four watt hours. You only hit that one hundred watt hour limit when you get up to about twenty seven thousand milliamp hours.
Twenty seven thousand. Okay, so my standard phone brick is well within the limit.
Exactly. And most manufacturers are starting to print the watt hours on the label now because they know people need it for security.
This has been such a deep dive into something I usually don't think twice about. It is amazing how much engineering and law is packed into that one little rule about not putting batteries in your checked bag.
It is the hidden infrastructure of safety. We only notice it when it gets in the way of our shopping or our packing, but it is the reason air travel remains as safe as it is.
Well, I think we have covered the bases for Daniel. Hopefully, this gives him some clarity while he is resting up on the couch. And maybe he can find a heat gun that comes with the battery already installed so he doesn't have to worry about the shipping drama.
Or he can just buy the tool locally and save himself the headache. But where is the fun in that?
Exactly. We like the weird prompts. We like the logistics puzzles.
We really do. And hey, if you are listening and you have found this useful, or if you have your own weird question about how the world works, please reach out. You can find us at myweirdprompts.com. There is a contact form there, and we love hearing from you.
And if you have a second, leave us a review on Spotify or wherever you get your podcasts. It really does help other curious people find the show. We are up to episode five hundred thirty now, and it is all thanks to this community.
It really is. This has been My Weird Prompts. I am Herman Poppleberry.
And I am Corn. Thanks for listening, and we will talk to you in the next one.
Goodbye everyone.
