That's pretty much how it used to work.

The main reasons why it changed are:

• Space, as a connector is slightly bigger than a soldered connection, and the battery itself has to be slightly bigger and stronger too to be safe to transport and handle without being protected by the phone's case.

• Water resistance; it's far easier to make a phone's case waterproof by just glueing the whole thing shut than having to use seals and gaskets and such to make it possible to open and close it at will.

LG had some phones like that in 2016ish, on the G5 the entire bottom of the phone slid out to reveal a big battery slot and on the V20 there was a button that let the metal back of the phone pop off so you could change the battery. I had an external battery charger and a couple of spare batteries for my V20, so I could just pack spare batteries and swap them whenever it got low. I never even bothered to plug my phone in, it was always just faster to pop in a battery that was already fully charged. It didn't have any water resistance, but it was a pretty small price to pay for endless battery life

It's a shame that LG's whole phone division went under, because they were making some of the coolest phones that came out that whole decade

I don't see an issue, but perhaps nobody ever thought to really try shipping a device with something like that. Specially since the water proofing advent.