"back in the day" we had waterproof phones with user replacable batteries, you could just buy another battery and replace it yourself. I have no idea why we can't do this now.
Power density and all of the problems that are fallout from high power density. A modern LiPoly battery contains a lot of energy. It's stored in a chemical that is highly reactive with oxygen, which you happen to be surrounded by at the moment.
Watch some videos on lithium battery fires. Not only do they have extremely hot flames but they spray out molten bits of battery and can't be extinguished with water.
To make a LiPoly battery that can be safely handled by normal people it needs a strong outer casing. A sealed battery in a phone uses the phone's case itself as the battery's protective casing. A user replaceable battery would need its own strong case. The phone then needs to be larger to accommodate the extra volume or have a smaller battery which stores less power than a sealed battery of equivalent volume.
The market has rewarded thinner phones with long lifetimes but also high performance. That triple point is challenging if not impossible to hit without sealed batteries.
Were they waterproof? I certainly don’t remember my Nokia 3210 being even splash resistant.
> I have no idea why we can’t do this now
For better worse I think the answer is quite simple - a combo of ease of manufacturing, a long term trend of slimmer devices that is broadly supported by customer behaviour, and an extra place to suggest a device upgrade instead of a repair. You’re more than able to get pretty much any smartphone battery replaced with a manufacturer similar spec these days, and people still choose not to do so.
Waterproof phones with replaceable batteries existed, but they used more rubber and other tricks to pull it off. This had the advantage of making it a lot easier to close the phone again and still keep the water resistant properties.
Having replaced the battery in my old phone, I sure understand why people don't "choose" to do so. The battery itself is worth maybe 20 bucks but the labour and tools required to replace it cost much, much more.
Compared to spending 30 bucks on a secondary battery back in the day, things sure have gone downhill since the days of user-replaceable batteries.
Please name these waterproof phones with replaceable batteries. None of my Motorolas or Treos were waterproof. I believe that harden phones may have existed but were not available to normal consumers. Maybe I’m wrong which is why I want to learn what phones you’re talking about.
The G'zOne made headlines being the first water resistant phone and it had a replaceable battery from the very start. The Fujitsu F-02D was another good example, with a fully-featured touch UI while still boasting something other than the slab-of-glass designs of today.
These phones weren't very popular in the west (Japan in particular had a large waterproof phone market, allegedly because people were taking them with them into the shower), but they have existed for a years, before the first Androids or iPhones became water resistant.
Phones like the Samsung XCover (the Android 2.3 one from 2011) were sold worldwide and featured a hotswappable battery. Over time these became bulkier and frankly uglier as they doubled down on how "rugged" they were, but the technology was clearly there.
Almost everything is splash resistant for some definition of a splash. I bet any modern smartphone does better than any dumbphone with buttons, because water can't permeate either of the big flat sides. If the water doesn't get inside, it can't cause damage.
"back in the day" we had waterproof phones with user replacable batteries, you could just buy another battery and replace it yourself. I have no idea why we can't do this now.