I mean some years ago Apple (or someone in the industry, don't quote me this is now just rumours and hearsay) that they intentionally optimized for about a day of battery life; the technology is there to make a smartphone last for a week, but that means cutting down on performance and whatnot.

I'm pretty confident that iOS 1.0 or 2.0 or whichever would last for a week on a modern-day iphone, even without all the optimizations they've done since then. Battery capacity tripled or quadrupled, and there's been multiple generations of chip design since then.