I would say, it is pretty darn good. My moms iPad still retained 58% of battery capacity after 8 years of use, without any battery swap.
My now sold 2018 iPad Pro after 3 years and 3 iPadOS updates, still had pretty good battery life.
So yeah, if you don’t need more than 8-10 hours a day, battery life on iPads is pretty awesome (huge battery + efficient OS + low power SoC)
I’d be interested to know how’s runtime on the 8-year-old iPad with 58% health, when compared to when it was new. That’s what I’ve been wanting to try. Unfortunately, my iOS version requirement precludes me from properly testing anything, but I can say one thing, even if my testing condition isn’t perfect:
My 9.7-inch iPad Pro retains the exact same battery life today than it did back in 2019 after being updated (same iOS version, 12). Of course, any comparison with the battery life back when it was new is irrelevant, iOS 12 is significantly worse than iOS 9, and there is nothing I can do to get that back, but I’ll monitor the situation on iOS 12, it’s the best I can do. So far... so good (relatively speaking, of course).
Yeah, I reckon three updates (like I’ve experienced) isn’t enough to completely obliterate battery life on an iPad. It won’t be like on its original version, but it will be good enough for many, probably still north of 10 hours with light use. Which is why what you say about your 2018 iPad Pro doesn’t surprise me, I guess it isn’t updated enough for it to really suffer.
8-10 is decent, and it always depends on usage, but for me that isn’t good. I can get 10-11 on my 9.7-inch iPad Pro with very light use, but I got 14 on iOS 9. I can’t get those three hours back, unfortunately.
What I am actually surprised about is some reports I’ve read of the first gen, 12.9-inch iPad Pro getting three hours on iPadOS 16, it’s been a pretty repeated complaint “look! I updated to the new iPad Pro from the first gen. It ran well, but battery life was three hours on iPadOS 16”. People never include many details, so it’s difficult to judge on that alone (usage? Gaming? Full brightness? Expected. Light web browsing and reading? Abhorrent). So I can’t draw any conclusions from that. It’s difficult to obtain results and screenshots by now because enthusiasts have moved on, so yeah. Difficult to know unless I test it myself, and I can’t because I don’t have them.
But yeah, I’d say that barring those 3-hour reports, battery life on iPads is half-decent (like I said, I wouldn’t call 10 hours of light use good, by any means), even several years after purchase. Whether there is an impact with perfect conditions (many years and cycles later, original version of iOS), remains to be seen, unfortunately.