yep I agree battery drain is REALLY bad! Also my 830 updated from 8.1 last night to build 10.0.10586.107 but now it says there's another update (build 10.0.10586.164) but it won't install fails with 0x800f081f.
Have you tried a reboot or a soft reset? Also, maybe check the Store for any updates or run the Upgrade Advisor tool again but it clears cache and it may delete the downloaded update and allow you to redownload it again.