Yeah, I've tried with and without BW and seen no issue that I can measure (i.e. whether I get an extra phone call matters more). But without exception I've had a one to one correlation with Pure Calendar Widget for 9 days now (5 with, 4 without, not all in a row either) and horrible battery life...and the widget isn't even on my home page.
Today, even with the longest phone call I've had, internet surfing, the usual high amount of emails (mostly deletions) some tapatalk posting, and taking some photos and playing videos for my daughter I was at 50% battery after 9 hours. Yesterday, with lighter use my phone died before that time, and the only difference was Pure Calendar Widget wasn't installed today..
I'm still trying to figure out if anything else could be contributing, but so far it seems pretty clear to me.