With phones with removable batteries, you could get extra large batteries with a replacement back cover. I had one for my Galaxy Nexus I'd slap on when I knew it'd be a long day.
Honestly that kind of turns your phone into a brick. With that being said companies shouldn't glue the battery in. If a user wants to replace it they should be able to get to the battery without having to pry it out.
It really wasn't that bad of a brick. Definitely still a bit of a brick and I received comments about it, but honestly you get used to it pretty quick.
Definitely not nearly as big as it would to put a power bank on the back of a modern phone over USB-C, maybe like 3-5mm more on the back side of the phone. It only doubled the battery thinkness, and that was a fairly thin phone to begin with.