SD810 is inefficient and generates a lot of heat. The more heat, the more battery power is wasted.
And my 1020 is the hottest device I've ever used. I can kill that battery if a few hours if i wanted. Heat doesn't prove your point, here.
Knocking the 810 for heat is cherry picking, anyways. We all know it didn't turn out as expected.
I have a feeling you're also completely ignoring some large factors. 1. Old devices used more efficient software. WP just isn't as efficient as it was, its not even close, really. 2. Less powerful devices are pushing WAY less pixels. Make an SD410 push a 1440p device and you'll see how awful the performance and battery life is. In the flip side, you take a device with an SD810 and give it a 720p display and it will last 2-3 days between charges.
Newer SoC's are nearly always more efficient. You just have to account for all the factors.
Posted via the Note 4/Nexus 7 (2013)/Lumia 1020/Lumia 2520