Rubber alone would require pressure pushing the battery against the housing to maintain the battery position during a drop. This pressure against the underside of the display module would mess with the display.

Adhesive is needed because there can’t be any pressure against the underside of the display module, and the battery can’t be allowed to move even a slight amount during drop impacts.

If this was true, phones with replaceable batteries would be impossible.

You can still put the battery in a box, and make it true inside the box.

The box takes up internal volume that could be used for more battery

In reality, replaceable batteries aren't glued inside some sort of box. Glue simply isn't necessary. It's probably just slightly easier to use a solution with glue instead of one without glue.

> If this was true, phones with replaceable batteries would be impossible.

They're thicker to account for a solid plastics barrier between the battery compartment and the display backside to protect the display from the user during battery replacement. Glueing the battery to the phone backplate allows the manufacturer to skip the .5mm of plastic.

Would anyone care if their phone was .5mm thicker?

I realize if this logic was applied to everything the phone could double in thickness, but for a consumable part like a battery, it seems worth the sacrifice to make the repair trivial for the average user armed with nothing but a small screw driver.

Most people already put their expensive thin phones in thick cases, so, no, besides dumb teenagers, I doubt anyone would care.

But simultaneously, I don't know if that many people would consider it to be selling point either nowadays. Battery capacities don't seem to shrink as quickly anymore, such that the phone probably gets damaged/stops receiving updates/is replaced anyway by the time the battery would need swapping.

Although perhaps that'll change now that the changes between even 2-3 year models are getting pretty small and software support periods are increasing.

It would be a lot more than .5mm and yes, I would care.

I will rather pay the extra 50€ in case I need to change the battery in a few years.

Except with a replaceable battery you can also have two batteries for emergency and get 100% charge in a minute when needed. This is what I do.

> Would anyone care if their phone was .5mm thicker?

People not, but marketing people do.

I don’t understand the mindset that marketing people somehow trick millions of users. Most of marketing is figuring out what people want and convincing them your product meets those needs.

There isn’t really a marketing strategy of “nobody values this but we will fight to the death to get the product designed that way so we can spend a ton of money convincing consumers to want something they don’t”.

Or, let me rephrase that, there is no sustainable marketing strategy like that. People do try (see: New Coke, Humane AI pin).

Marketing people love some metric they can use to differentiate from competition. A phone gets thinner, lighter and survives more fall height or water depth. A PC gets a faster CPU (anyone thinking back to the megahertz wars [1] or the gigahertz wars [2]?), a bigger SSD or more RAM.

[1] https://collections.museumsvictoria.com.au/articles/1538

[2] https://arstechnica.com/gadgets/2024/03/intel-revives-the-mh...

Phones with replaceable batteries use plastic, and people really hate plastic (they use "cheap plastic" as a synonym for "plastic"). So they rather buy a phone that is a little bit slimmer and has a glass back.

(Manufacturers probably also like phones that have to be replaced in a few years due to battery age.)

Because the volume it takes up could always just be used for more battery instead

Not impossible, just less durable. See also: sockets instead of soldered chips, connectors instead of soldered wires.

Phones with replaceable batteries typically were more durable, not less. Though that may have to do with using plastic cases that are more durable than glass.

Also batteries under pressure is a dangerous and bad idea

I think they want to leave some space so that the battery can expand. Easiest way to do that is to glue it on one side and leave a bit of space on the other side.

I love how they learned from their mistakes of the old macbook pro. Batteries need ability to expand ever so slightly. Same reason why cranes are able to move freely with the wind when not in use.

Huh. I had no idea cranes are allowed to freely rotate with the wind. Makes sense, just one of those things I'd never thought about.

Neat!

Why not add a valve? Every cylindrical cell has one, but manufacturers seem to be allergic to adding one on lipo packs. Apparently having them swell to 5x the size and break the device casing is preferable.

Lipo battery gas contains flammable and poisonous chemicals - including Hydrogen fluoride. Swelling slightly in normal use and occasionally rupturing is safer over-all than off gassing all the time.

From wiki:

> Hydrogen fluoride is an extremely dangerous gas, forming corrosive and penetrating hydrofluoric acid upon contact with moisture. The gas can also cause blindness by rapid destruction of the corneas.

https://en.wikipedia.org/wiki/Hydrogen_fluoride

Okay I’m really going to prioritize throwing away my old android devices now.

Throwing away is a real hassle. You often buy a new phone because the old one is broken. So data is on there but you cant turn it on. Get a drill out? Not sure I want to breath in that dust.

Microwave? Might be easier to avoid the fumes than the dust from drilling. Probably easier to drill outside and wear an N95 mask and goggles though.

Just put a soldering iron over the epoxy on the ssd chips, get it really hot to ensure the sillicon gets heated to at least 100C and your data will be gone forever in a completely non-functional chip.

Buy an iPhone and don’t worry about recycling it because storage encryption means it doesn’t matter. You can never plan for when you might lose a device.

No! Take those devices to electronics recycling. They DO NOT go into your municipal trash. Lithium-ion batteries can start fires inside your garbage truck, forcing the truck to dump its flaming contents onto the street. Electronics contain hazardous materials. And electronics contain valuable materials worth recycling. Where I live, it is illegal to put electronics in your municipal trash.

Most laptops use cylindrical cells for their battery pack, each one with a valve. I really doubt this is any kind of actual problem, more like an excuse given to reduce costs at the expense of the consumer.

Standard lead acid batteries in every car and UPS also release H2S in vast quantities when old and charged, and nobody seems to care.

> accasionally rupturing

You know this is most likely results in a fire right? There is no case where even a slight chance of it happening is safer.

Can you name any current laptop model that uses cylindrical cells? I haven't encountered any cylindrical cells when opening a laptop in well over a decade.

My old G771 definitely has them, though that one is like 8 years old or so now? Yeah they mostly do lipos these days for thinness and weight reduction, I'm sure some gamer laptops still run on 18650s. I wouldn't really ever buy a laptop with a lipo myself, shit's just gonna inflate and split it in half.

It's not just laptops anyway, EVs, power tools, flashlights, power banks, li-ion drop in replacement car/ups batteries. Anything that has a lipo has at some point had a cylindrical model too.

I'm not questioning whether cylindrical cells used to be popular for laptops; they were an iconic part of old ThinkPads. But I've opened up plenty of chunky gaming laptops in recent years from Asus, Dell/Alienware, MSI, Razer and have seen nothing but LiPo batteries. I think cylindrical cells may have genuinely disappeared from the laptop market at this point, unless they're still around in some niche that's significantly more obscure than big heavy gaming laptops. Most laptops these days that opt for a thick enclosure are doing it for the sake of the cooling system, not for the sake of fitting in a thick battery.

Edit: I looked at the Gigabyte A5 and agree that it's probably using cylindrical cells. It appears to be a Clevo system, so there were probably other brands reselling as well. But it's not quite a current model (3 year old processor), and the reviews seem to agree that the battery is one of the worst things about the machine, because the capacity is way too small for that class of machine.

Pretty sure the airtight casing is here on purpose to trap flammables gas a dying cell create. Without it it would be very unsafe to use this type of batteries.

A container that traps flammable gasses is called a bomb

This is not usually a design goal

No, a container that contains flammable gasses and then destructively allows them to escape is a bomb, one that just inflates is arguably the equivalent of a self inflating pillow.

Gasses create pressure A phone casing is not a pressure vessel This isn’t going to work

I guess using cylindrical cells in power tools, laptops, electric bikes and cars, power banks, flashlights, etc. must be super unsafe then, since they all have valves that release gas instead of inflating.

A valve is a one time only device to prevent an explosion in the event of thermal runaway. It’s not going to accommodate the slight expansion and contraction which are a normal part of the charge cycle for lithium batteries. If the battery is kept under mechanical pressure in order to avoid movement (without the use of an adhesive) then there is no place for the battery to expand to. That sounds like a recipe for disaster.

The rubber mat is only going to work if the battery is pressed against it with a lot of force. An adhesive will hold with no pressure at all.

My guess is that even the tiniest movement would wear out the battery's casing.

Size, adhesive is thinner than any kind of physical layer surrounding it. I would presume as well it's better for thermals for allowing heat away from the battery.

Drop protection is one of the main reasons, especially when you use batteries with soft shells.