I also have an Ativ S that shipped with portico, and I had a strange battery drain on I think Wednesday morning. I took my phone off charger at 5:42am, read a chapter of Youversion over breakfast, spent 10-15 minutes on the web, listened to about 45 minutes of music on my commute, and then shut my data connection of when I got to work, as I have little to no signal there. All ust like every other morning of my work week. And just like every other morning, my battery was sitting at 99% when I shut my data off. (about 6:50am; shift starts at 7am) This morning, however, my battery, instead of draining a maximum of 1% between then and noon like every other morning, decided to plunge to 65%, where it stayed until the end of my shift at 5:30pm. I listened to music again on my way home, and proceeded to use my phone just as hard as ever until I went to bed. It still had 25% remaining when I threw it on the charger at 9:30. (it's usually over 40% on a work night) It hasn't happened since; battery has been stellar as usual. Tonight I put it on the charger at 2am with 45% remaining after the usual 5:50am start but only an 8 hour work day. This means I was home and on it hard from 3:30pm. Like I said, strange...
UPDATE: Ok so today I checked my phone battery at noon and it was at 92%. Without touching it, and it being in airplane mode the whole time, it was at 26%. I thought "this has to be a mistake" so I soft reset it. When it booted back up, it was at 15%! Today marks the first time I've EVER charged it on the way home from work. I hope this doesn't happen again... Bizarre.