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.
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.
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.
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.)
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.)
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.