I like computers, trains, space, radio-related everything and a bunch of other tech related stuff. User of GNU+Linux.I am also dumb and worthless.My laptop is ThinkPad L390y running Arch.I own RTL-SDRv3 and RSP1 clone.
SDF Unix shell username: user224

I used to carry 2 batteries. Though that's probably not a large market. But if made around that idea it could be done well.
Either having hibernation or some power source to keep the RAM powered during main battery swap (small supercapacitor, small regular Li-Ion battery, thin lithium ceramic battery, I don't know what's best), and a dock for battery charging.
Kind of like LG G5.
Preferably, the battery would have integrated charger so you don't have to carry around a dock. Just what you do now, just with the spare battery replacing a power bank in more convenient way. Maybe it could come off with the charging port just like LG G5, but it would be built-in rather than being something you pop a different battery into.