It didn't jump up suddenly; there were many software improvements in regard to battery life deployed through the years which together sum up to a pretty significant change.
There's not much difference in battery usage between hardware batches, the improvements were mostly in software. The battery capacity has changed though - the earliest batches that some early backers opted to receive had a 2000mAh battery, while later ones had 3600mAh one. The mass produced version ended up with 4500mAh.
The early batches shipped with early software, and that was actually the biggest contributor to bad battery life and (now long solved) overheating issues.
Okay so some people don’t even have the latest hardware revision so they’re stuck with a phone that will never support suspending and will have terrible battery life forever?