Feel like it’s probably better to continue this little off shoot in this thread unless there’s somewhere better off it since it’s not really related to Chase.
I do a fresh install every major release. New devices are always set up as new, no restoring from backups (don’t even have backups turned on).
Don’t run the iOS betas on my personal devices either, which includes my phone where I use Monzo.
I suspect like Safari, how we use the app and what’s going on inside it will impact how much battery it uses too. My time is largely spent in trends. When I’m opening the app it’s more of than not because of a notification or to check on my balance tab in trends (where I will usually play with the slider a bit because the haptics make it fun and I’m a fidget toy person). That’s probably more intensive than someone who opens it to check recent transactions and closes it again.
The current Trends performance issues might be playing a role too. The crashing bug has hopefully been fixed now (thanks @leewatkins!) (which I should probably now mark as the solution to my thread!) so that shouldn’t be affecting things anymore! There is a memory leak (I think) somewhere though, which more folks than just me are experiencing this time and I’m having to use the reset section every few weeks or so when the app becomes unusably sluggish and unresponsive. Phone gets hot in this situation too, so no doubt is something else impacting battery life.
The battery life hit from Monzo is not significant enough that I consider it an issue per se, but it’s not as good as I’d normally expect for a banking app either. It’s not terrible, it just feels like it’s not been properly optimised for later iPhones models and iOS version to keep it as efficient as it probably could be. The most visible representation of that is how the app was never, and still hasn’t been updated for the new iPhone screen sizes. It’s very hard to see, but the interface elements are ever so slightly larger in Monzo compared to other apps because of it. I’ve posted about that somewhere on here before too. Most people will probably never notice it, but it’s something I can always see whenever the keyboard comes up and it throws me. I can touch type the way I type on a mechanical keyboard (from muscle memory so I don’t need to see the keys) and remain very accurate. The very subtle change to the keyboard in Monzo’s app vs most others that have since been updated really throws that into whack and I can’t type anymore.
Edit: here’s where I’ve mentioned the screen size thing before, with screenshots that capture the very subtle difference:
Edit 2: off the back of remembering this, just decided to test it again to check it was actually still the case, and it does appear, that at least the core iOS elements are no longer scaled when comparing side by side in Pixelmator to the mail app. 
no idea when they actually fixed it, but this is why apps benefit from usefully detailed release notes! I had no idea it had been fixed.