Hey,
I just wanted to share something that I noticed today related to the sudden-battery-death (well, 4%) bug.
First some background :
I left from home in the morning for a trip with fully-charged N9, turned on Drive to see the distance to the destination and forgot it on. Once arrived, I checked the time and noticed Drive was still on (and GPS with it). "**** there goes my battery" was my first thought, and in fact, half of it was gone. I turned Drive off.
Then during lunch time, after some minor netting with 3G, the N9 alarmed me of "battery low" (from the half level that it was *before* i started navigation a first time). An sms followed (second notice of battery low), and a call (third and fourth notice in a row).

The phone had 4% battery left, 8 minutes talk time + 2 hours standby time.

Now to the intresting part.
I figured it was a good chance to test my "power saving mode level fix", by changing the power saving mode level, which -at that time-
was at 10%. I move the slider to 60%, putted the phone on stand-by, and restored it then back to 10%. No help.
"oh well" i thought, locked the screen and dropped the phone in my pocket. no necessary usage anymore.

Fast forward to about an hour ago, I check my phone for an SMS. Battery level was 27%! Wtf?
Level is *still* 27% (phone was in standby).
Remaining talking time, 1 hour 28 mins, stand by time 1 day.

Bug in power management? Sounds more and more like that to me!