For that matter, I put a chonky case on my phone anyway... would rather have a sturdier phone that doesn't need an additional case that has the features I'd like, including an easily replaced/swapped battery.

Beyond this, hell, make the "internal" battery solid-state with minimal capacity and have an external power pack from the get-go as part of case designs. Get the size of battery you want... if you want a big booty phone with battery for days, you can get it.