I hope that this remains true for every model when iPadOS 26 is released, because the history of standby battery life has been funny for me.
Standby battery life was amazing at the beginning. Speaking only about original iOS versions, all 32-bit iPads had amazing standby battery life. You could leave them on standby for a week and they’d barely drop. I then upgraded to the 9.7-inch iPad Pro on iOS 9… and that did not change. Standby battery life was amazing. Three years later, and Apple forced that iPad from iOS 9 into iOS 12. But guess what? It has (because it still runs iOS 12 today) the same amazing standby battery life it had on its original iOS version.
Then it fell apart. I upgraded, three years ago, to the device I’m typing from: an iPad Air 5 whose original iOS version is (and still runs) iPadOS 15. Standby time? Utter and complete garbage. It keeps dropping and dropping. Four, five percent in less than 24 hours. It’s awful. Really awful. I run extremely efficient settings, and I could never identify the issue. Talking to people here on MacRumors, I realised that everybody has the same experience, so it must be the OS itself.
But then I “side-graded” to the 11th-gen iPad on iPadOS 18. That one isn’t as good as earlier iPads, but it is FAR better.
A similar story happens with iPhones, but with a different cut-off point: amazing at the beginning, up until my iPhone 6s on iOS 10. I didn’t use iOS 11, but I have an iPhone Xʀ running iOS 12 and standby time has always been utter garbage. Like the iPad Air 5, it just keeps dropping. I upgraded to my 16 Plus on iOS 18, and it is FAR better. Go figure..