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Comment by muststopmyths | Hacker News Reader

> never having heard not to put a battery in checked luggage

Maybe not conventional batteries, but you've been disallowed from putting lithium batteries in checked luggage for at least 16 years. I remember being dragged into the bowels of an airport by security to open my checked bag because I'd forgotten a device in it. That was in 2009.

When you check in bags they ask you to make sure there aren't any rechargeable devices or battery packs in them and this has also been going on for a long time.

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> “you've been disallowed from putting lithium batteries in checked luggage for at least 16 years.”

This rule only applies to loose (spare) Li-ion batteries, not batteries which are installed in a device.

Batteries over 160 Wh (in some cases, 100 Wh) are banned whether they’re in a device or not, but that’s far bigger than any phone battery: an iPhone 16 Pro Max battery is about 16 Wh, and typical laptop batteries are around 60 Wh.

IATA Li-ion battery fact sheet: https://www.iata.org/en/iata-repository/pressroom/fact-sheet...

Notably the 16” MacBook Pro (every model since 2019) goes right up to the 100 Wh limit.

For comparison, 100 Wh is 360,000 joules, which is just under either the energy released by explosion of 100 grams of TNT, or the kinetic energy of a small car at highway speeds, or the kinetic energy of 1 gram meteor hitting Earth.[1] (Sorry, I've never been a fan of the "Wh" unit and so wanted to put that total energy into layman terms.)

[1] https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)

Or a McDonalds medium fries?

EDIT: doh, just realised you were comparing with other forms of damage. That said, I think its truly amazing that a snack has the same energy as a nasty car crash. Mind blown.

That is, 100 Wh = 86 kcal.

Enough energy to heat 1 kg of water by 86°C (or 86 kg of water by 1°C).

To me it is hard to visualize how much damage the total energy gained from digesting chemical bonds of food could do to an airplane. I can better visualize the damage that could be done by a highway car crash or detonating a handful of TNT in an airplane.

These counterfactual comparisons are a slippery slope and not as helpful as you think. I hardly think that you, I, or most others have an intuitive understanding for what happens when a 1 gram meteor hits earth. Have you ever witnessed that?

The average failure state of a battery is not similar to detonating a handful of TNT on an airplane, which is a more instantaneous explosion. Sure, some battery failure states are violent and would unquestionably be a cause for an airplane to call a mayday and land, but something like puncturing a soft-cell battery is still a slower release than TNT.

We should just expect people to get better at understanding useful units — I'd prefer someone learns Wh since it is indeed a useful metric—kWh is the usual major unit of energy at home, and Wh is just smaller than that.

I was trying to guesstimate a theoretical upper-bound on the damage. Looking at youtubes online, it seems a labtop battery explosion is still scary and more like a handful of firecrackers than TNT, but what actually seems worse is that the explosion is followed by the labtop being on fire and producing subsequent smaller explosions. So the worse case is that the fire ignites other stuff in the plane, which includes other lithium batteries.

Can the battery actually release that energy as explosively as the TNT can? I mean under normal corcumstances, not maliciously modified.

(100Wh / 3.7V ~= 27000 mAh, 160Wh / 3.7V ~= 43000 mAh. Wh represents theoretical total energy, used as a normalized comparison, and Ah is used to practically determine max safe charge/discharge rates)

This rule only applies to loose (spare) Li-ion batteries, not batteries which are installed in a device.

I've heard of people ordering 18650s online and getting them along with a free flashlight in which they came; I wonder if this regulation is why.

Almost definitely for import tax/restriction reasons. Putting the battery inside a cheap flashlight places it in a separate category than a battery by itself. Felt on the bottom of Converse sneakers to classify as slippers is a classic example of this.

The battery limit described is for individual passengers, not air freight.

Air freight for Li-ion batteries is pretty strictly regulated too, especially when the freight is carried on passenger aircraft.

See UPS Flight 6 for a very good reason about why the flight of lithium batteries is regulated

As always, Admiral Cloudberg has a deep-dive into this crash: https://admiralcloudberg.medium.com/alone-in-the-inferno-the...

Slightly off topic, but she does an amazing job.

I watched both Mentour Pilot and Green Dot Aviation's videos about it. Mentour Pilot's video terrified me, as it simulated the audio of being inside the cockpit, with GPWS, fire warnings, the sound of the fire all going on at the same time

Green Dot Aviation: https://www.youtube.com/watch?v=T7uw6VzWHcM

Mentour Pilot: https://www.youtube.com/watch?v=Y50saxfTqQA

Yup, any time I order anything from Amazon that has lithium it comes with a big warning sticker about shipping restrictions. Even if it's a fixed battery inside a device.

Indeed. If it’s sold as already in a device, it doesn’t need the battery sticker and in general the regulations around shipping it are significantly less onerous.

many laptops are reaching 100wh limit, dell xps 16 has 99.9wh iirc

And people dont travel with single device anymore. My usually setup has 72wh powerbank, ~20wh phone and 90wh laptop, and various smaller gadget. They are reaching nearly 200wh

Interesting, at the airport I always see general "no (devices with) batteries in checked luggage" signs.

One time I had an old phone with battery removed in checked luggage and when I arrived at my destination, I saw they fiddled with the tsa lock and the phone was taken out of the envelope I had it in and just lying on top of my clothes. I mean maybe they saw it in an xray and wanted to steal it and then saw it was some old junk phone, no idea how good the xrays come out to tell beforehand whether you're dealing with an iPhone or 7 year old android midrange...

I also thought the reason you couldn't travel with unattached spare batteries was because something could bridge the + and - and create fire from a short, not because they were lithium. Like, traveling with my little power bank wasn't an issue because it's all enclosed.

I still send my AirTags in checked luggage. But they are small!

Checked baggage is actually one of the better use cases for AirTags.

AirTags also don’t use rechargeable lithium batteries.

Aren't non-rechargeable batteries still at least a little dangerous, though?

They're more dangerous. The reason lithium-metal batteries are "non-rechargeable" isn't that recharging them doesn't work; it's that they have an unacceptable probability of exploding during the process. Other forms of electrical, thermal, or mechanical abuse can have similarly spicy results.

Spare non-rechargeable lithium batteries are also forbidden in checked luggage[0]. AirTags are allowed because the battery is installed in a device, though Lufthansa briefly tried to argue otherwise after some bad press involving passengers finding their own lost bags[1].

[0] https://www.faa.gov/hazmat/packsafe/lithium-batteries

[1] https://arstechnica.com/gadgets/2022/10/lufthansa-awkwardly-...

When people say “Lithium batteries” in this context, they mean lithium-ion rechargeable batteries.

AirTags contain lithium primary batteries, which are a totally different thing (other than both containing the element lithium).

Lithium primary batteries present no more a risk than alkaline AAs. Probably less.

They are more dangerous. They contain significant amounts of lithium metal, the thing that bursts into flames when in contact with water. There are similar restrictions on them for air travel.

> They contain significant amounts of lithium metal, the thing that bursts into flames when in contact with water.

How does that tell you that they are dangerous? The danger with rechargeable Lithium batteries isn't that they contact water and begin to burn.

Last time I ordered some lithium primary batteries from Amazon it came with the lithium sticker. I didn't look into the rules.

Lithium poses two risks:

1) The internal resistance is low enough that if it's shorted it can go into thermal runaway. This is the risk they had in mind when saying no loose cells (but note that cells merely need to be securely contained, not specifically in a device.)

2) Secondary cells can grow whiskers inside the cell. If a whisker grows just wrong it can short the cell from inside and drive it into runaway. This is the risk that they are worried about here--and it's a legitimate risk, it's brought a plane down.

The reason the rules are different in the passenger compartment is that while there's nothing on board an airplane that can fight a lithium fire it's generally a small, weak fire (the big e-bike batteries that have been in some rather dramatic videos aren't allowed) that humans can generally keep from turning into a big fire. But if nobody can fight the fire you have a big problem. Hence why lost phones are treated very differently--they could have fallen someplace where the fire wouldn't be fought.

> When you check in bags they ask you to make sure there aren't any rechargeable devices or battery packs in them and this has also been going on for a long time.

Literally never once have I been asked that and I flew internationally 6 times a year for more than 5 years.

The only thing I can think of is maybe you look like the kind of person that would have rechargeable devices and battery packs in his luggage? :)

Before you accept your plane tickets you get asked question about illegal hazards you are flying with. Lithium batteries are clearly noted. Maybe you are just skipping that notice because you assume you are not a hazard? :)

This definitely happens stateside. Usually during check-in

They had to pull my checked bags once because I couldn't find an 18650 when they asked me about carry on batteries for a puddle jumper the last time I flew, which was nearly a decade ago at this point. They definitely care. The passengers are also supposed to care.

People who don't care are the reason I don't fly anymore.

I see a warning about rechargeable batteries in checked in luggage almost every time I check into a flight. I wonder what explains our difference of experiences. Maybe it's the fact that I mostly do electronic checkins vs just showing up at luggage drop off.

Luggage drop-off asks the same question, here in Australia anyway

I also see this every time I check in for my Air NZ and Jetstar flights here in New Zealand. But I suspect like many I just by habit press 'No, I don't have any hazardous things to declare.' to move to the next stage of the check in process as quickly as possible! There are also signs and stickers on check in desks for those checking in manually -- but not sure how good the agents are at bringing people's attention to that.

I do get pulled aside for "enhanced screening" consistently while transiting Europe :-)

I'm sure you didn't actually mean it that way though :-)

A sibling comment made me recheck the rules and it does seem like phones and other small rechargeable devices are allowed in checked baggage.

Maybe I've been unconsciously extending "power banks and rechargeable batteries" to also mean device when questioned.

Except that one time in Latin America where they would only let me put my ultra-compact camera in checked baggage if I took out the batteries.

Yeah, I’ve been aware of this for ages. That said I’m sure lithium batteries in checked luggage are super-common in things like electric razors and tooth brushes and a ton of other things we never think about.

It’s like airplane mode. How many cellphones on a given flight are actually in airplane mode?

A phone not in airplane mode and a high capacity lithium battery are not comparable at all.

Airplane mode is largely pseudoscience/an abundance of caution/solving a different problem than a safety one. There's approximately zero chance of a phone interfering with avionics, especially modern ones, with their very low transmission power.

Supposedly the real reason has always been that mobile network operators don't like the interference high-altitude phones can cause: They're in view of potentially many base stations, some of which might be using the same frequency (which is possible since far-away regular-altitude phones are below the radio horizon and therefore not an issue).

Some evidence for this theory: The "mobile phone ban" is an FCC regulation, not an FAA one, and many (non-US) airlines have been offering on-board microcells for decades without any issues.

"the real reason has always been that mobile network operators don't like the interference high-altitude phones can cause: They're in view of potentially many base stations". This makes zero sense: the aircraft is on the ground and not moving when the ban is put in place. The ban is removed at altitude, when, you say, that the phones are potentially 'in view' of many 'cell towers' (not base stations). In fact, the plane is essentially a Faraday cage at altitude, and a phone has almost zero chance of connecting to a tower, even shoved into a window pocket.

> The ban is removed at altitude

Not in the US, where it applies throughout the flight.

And at least in Europe, the ban is due to the risk of distraction/disorientation in case of an emergency, in my experience.

> the plane is essentially a Faraday cage at altitude, and a phone has almost zero chance of connecting to a tower

Counterpoint: I have a whole collection of “welcome to <place>, your roaming charges will be <exorbitant>” text messages on my phone from countries I’ve only ever overflown at 30k feet.

This is from flights that do permit in-flight phone usage, but I believe my network has no roaming agreement with the microcell operator, so it keeps scanning and sometimes catches a bidirectional link to some long-range tower. (They’re specifically optimized for that in the North Sea and Atlantic for fishing boats, as far as I know, so for regular modern towers it’s probably less likely, but that separation hasn’t always existed.)

Supporting your counterpoint: I am a cell tower geek and I have an app on my phone that records the cell ID of every tower my phone attaches to. I once flew from Wellington to Auckland on an Airbus 320 and forgot to turn off Airplane mode. Arrived into Auckland and my app had logs around a hundred or so cells my phone managed to attach to. So it can happen. I've also had successful two-way text conversations while still in the air but low enough (e.g. when descending on approach to an airport). Saying a plane is a Faraday cage is a bit extreme but I do acknowledge the steel tubing around you will reduce the signal strength by quite a bit -- but not quite enough to 100% block out the signal it seems.

Plane windows are large compared to radio waves. They'd need to be no more than about 5 cm wide to create a full Faraday cage.

Supporting your counterpoint too: MH370 co-pilot's mobile phone did connect to a cell tower mid-flight after the hijacking. [0]

[0] https://www.dailymail.co.uk/news/article-6839167/MH370-pilot...

Is a lithium battery installed in a device (allowed) comparable with a lithium battery not installed in a device (not allowed)?

That's the steelman version of the parent poster's question.

Danger probably primarily varies with capacity, production quality etc., not form factor (disassembled or assembled into a device), sure.

I'm not saying that current regulations of lithium batteries make sense; my argument is that the actual threat from lithium batteries seems larger than that of devices not in airplane mode (i.e. somewhere around zero).

An installed battery will have its terminals protected and connected to the device.

An uninstalled battery will have its terminals exposed, where they could be accidentally shorted by a stray paperclip, foil wrapper, or zip.

There's also the issue that the burden is on proving they're safe--and nobody has a reason to shell out the bucks to do so.

I do agree that interference is quite relevant. The general rule of radio is that you play nice, especially when on a licensed frequency (the cell companies have the licenses for those bands, the users do not), and a phone up high over multiple cell towers is most certainly not playing nice.

Small Li-ion batteries installed in a device are allowed in check luggage.

Loose/spare Li-ion batteries that are not installed in a device, and large batteries over 100-160 Wh are banned in checked luggage.

It's unclear to me what the official requirements are. For example this is from the TSA's site:

"Devices containing lithium metal or lithium ion batteries should be carried in carry-on baggage. Most other consumer electronic devices containing batteries are allowed in carry-on and checked baggage."

Taken literally, this is of course widely ignored. There are also various requirements around spare batteries that do include capacity limits.

Yup, it's happened to me. I had put the battery in my daypack while we were there. I thought it had gone back in my laptop bag for the flight--nope, it was buried in the daypack. PVG security caught it.

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