When the notebook is off (and of course unplugged), the battery depletes completely in 5-6 days (it looses about 15% of its capacity each day).
I noticed this behavior when I bought the laptop (in Nov 2016), but it didn't bother me at that time because I used the computer on battery during the day, and recharged the battery overnight. I also naively thought a solution would be found, and I'm now surprised to find this isn't the case.
However now my work and habits have changed, and when I'm on the road, even if I use the computer for a few minutes per day I need to bring the charger and find where to plug it, otherwise the Spectre x360 is just unusable because of the battery drain.
The BIOS and drivers are all up to date. As many other customers have already noticed, this drain issue has never been solved by updating BIOS and drivers.
I have been a Dell customer for the past 15 years and this is my first HP notebook. I must say that other than this drain issue, I'm rather happy with the performance of the Spectre x-360. However, unless the HP Customer Service solves the issue (and free of charge -- the warranty has expired, but the problem is well-documented), this first HP notebook I bought will very certainly be the last.