Power banks for tramping

Lately I've been updating electrical devices (torch, gps, camera are my main three). More and more they're trending towards charging and/or running straight of USB, whether or not they have replaceable batteries. I used to try and always get stuff that ran off AA batteries to make it simpler to manage spare power between them, but now it's making more sense to have lighter devices and carry a power bank instead. I presume many people here are already doing something like this. I haven't bought one for a while, though. With a tentative look there seem to be lots of power banks out there, but much of which also looks very consumer grade and aimed at people are are just hanging around town and worried about their phone battery running out. Are there any favourites out there for tramping purposes, or thoughts on what might be good value for money? In my mind I'd like something reliable and reasonably durable, like if I knock it or if it got a little wet then I'd want it to keep working. Weight's always of interest, as is having a decent charge and some kind of indicator of remaining charge. I'm not expecting to get it perfect first time, but I might as well try. Any thoughts?