It's often times hard to understand exactly what Phoronix is talking about,but this article is fairly clear

I have been advising people to upgrade to the new ,38 kernel but I had noticed that my charge did not last as long; I thought it was just my usage pattern having changed thanks to the updates in the new kernel.  Come to find out that's not the case.  Best bet I guess is to keep a >,38 kernel for those times unplugged from the wall.

**edit**

Never again will I use that quick topic option.

i had to read through this a few times before i figured it out, but i haven't finished my first cup of coffee yet! ;>} when i saw 'mobile' and 'kernel' i immediately assumed you were talking about another problem.

i tether to my phone with bluetooth to use gprs when not in wireless range, and i have had to downgrade my kernel to 37 (twice already). happened on first release and then i tried again when rev3 came out but no luck. apparently the kernel firmware for my atheros chipset breaks bluetooth. guess i finally have a reason to compile my own kernel! (@urandom) ;>}

k

Follow up to this on Phoronix again.

Quick explaination was that apparently there was a patch to disable ASPM (Active State Power Management) unless the bios implicity allowed it. Hence PCI-E lanes run at full power whether they need to or not. For desktop users this is not really an issue (in fact with the latest Sandy Bridge processors, and their relative dearth of PCI-E lanes, paired to a high end card this would seem to be a net benefit) but for mobile users it was killing battery life.

Apparently 15% or so decrease in power usage (and corresponding increase in battery life?) results in simply including in your boot line the following:

pcie_aspm=force

I'm going to play around with that option when I get off work and see how well it does...