Got a (replacement) 920! What should I do now?

Hello, Tribe! I am the guy from this here post. I went back to the store and they gave me a replacement handset.

Now that I am starting afresh, what should I do? So far, I have drained the battery from whatever it was in the box, and then I charged it back to 100. I am currently draining it.

How long should I cycle through this?

How long should it take for the battery to become stable?

How long should the runtime be for this phone? (so far, it has lost 20% in 1.5 h).

When should I install 8.1?

Thanks for all your help guys!

Its really annoying that I have to consciously take care of the battery on this phone. I do not wish to understand what it must be like for non-tech-savvy consumers. (I hate to be that guy, but my girlfriend's iPhone 4S seems to work better out of the box than my phone - both this replacement and the previous one)