Or device battery life was shorter because we hadn't developed better battery technology or better power management

You talk about the misaligned incentives of replaceable batteries but fail to point out the incentive built-in batteries: need to replace a battery, buy a whole new device.

My points are about what it’s like current with removable batteries in cameras with current technology. Battery usage is dependant on usage to some extent. For casual use my cameras last weeks on a battery and even shooting all day e.g. in a studio, I would only get through one battery. Modern cameras also have usb-c charging and can be used whilst you do that, so that’s an option too, though less practical in my view. Yes, camera batteries are proprietary and it would be better if they weren’t, though they are generally the same across similar cameras from the manufacturer and the same in the successor cameras. Many mirrorless cameras are water resistant (with the right lenses) so the can be used in heavy rain, though not under water without a housing. Action cams like the GoPro 13 Black are waterproof with a removable battery.

My headlamp is waterproof and it has a replaceable 18650 battery without needing to dab silicon(e?) on it. It is also rechargeable over USB type-c so I have both the option to replace the physical battery or plug it in to charge that battery.

> My Canon waterproof camera came with a tube of silicon I had to dab on the battery compartment gasket

And those devices are MORE water resistant than most phones. The grease is to improve ingress protection beyond what's possible with double sided tapes used in "waterproof" phones. And the manuals for that gear should mention a retention period of x hours under y depth counting down from the moment the housing was closed.

Contrast to that, waterproof ratings for most glued-shut waterproof phones are invalid after purchase. Out of package, out of spec. Most manufacturers don't honor warranties for water damages for waterproof phone, and very few offer requisite gasket maintenance to retain waterproof ratings.

Apple doesn't have a recertification option even for battery replacement at Apple Store. Do ANY service and it's invalid. Not waterproof even in THEIR hands. Frankly their terms is one of the most egregious.

Headlamps for sensitive applications will ALWAYS involve a replaceable or external battery. Can't have your light going out when you are in a dangerous situation. When I used to rock climb, I always kept 3x AAA's taped to the strap in case the one I had in died. Never needed to use them, but made me much more confortable.