MBP (13-inch, early 2011) goes into hibernation instead of safe sleep upon closing the lid (only when using battery power)

Question

MBP details
13-inch MacBook Pro, early 2011 (model identifier: MacBookPro8,1)
Running Yosemite, OS X 10.10.1 (however, problem started while using Mavericks)
2.5 GHz Intel Core i5
4 GB memory
Symptoms
* the MBP goes into hibernation instead of sleep upon closing the lid on battery power (i.e.,  when AC adapter is NOT connected)
  -- problem does not occur when AC adapter is connected
* putting the computer to sleep by other means does not induce the problem; these other means include:
  -- [i] option+command+Power,
  -- [ii] Apple Icon --> Sleep,
  -- [iii] in Terminal: pmset sleepnow
* the battery is NOT getting drained at all; if I close the lid on 87%, the battery is still at about 87% when I get the MBP back up and running
To be as clear as possible:
(1) MBP is on and in use  (power source: battery); battery is at X%
(2) the lid is then closed
(3) the battery indicator light glows bright for about 10 seconds, then shuts off, and with it so does the MBP (all fans and sounds cease)
(4) opening the lid and pressing any key on the keyboard does nothing (the computer is not sleeping)
(5) to turn the MBP back on, I must hit the power button once; this brings up  and the gray screen and loading bar indicative of returning from hibernation
(6) log in; battery is still at X%
Attempted Solutions / Fixes
There are Apple Discussions addressing similar MBP issues, many of which at least have work-arounds, if not full-blown solutions. However, I have tried many of the proposed work-arounds and solutions; nothing has solved my problem. Such attempted solutions include:
  * made sure EFI/SMC firmware was up to date
  * updated all software
  * logged in as a different user
  * booted in Safe Mode
  * reset the PRAM
  * repaired disk permissions using Disk Utility
  * repaired additional disk permissions in recovery mode (a la this chron.com advice)
  * ran the Apple Hardware Test multiple times (short test while plugged in, short test on battery, extended test while plugged in, extended test on battery)
  * booted from an external known-good OS on USB drive
  * reseated the RAM
  * used MemTest to test the RAM's health (it was good)
  * tested my battery's health with the app Battery Health (it is healthy!)
  * booted my computer with one stick of the MBP's original RAM at a time (figured "why not?")
  * booted my computer using other sticks of RAM
  * checked my power management settings using PMSET in the terminal (e.g., pmset -g); tried various hibernation modes (e.g., sudo pmset -a hibernationmode X, where X=0,1,3, etc)
  * searched/grepped through my power management logs and Console messages to look for googleable items (e.g., pmset -g log | grep WORD, where WORD=failure, sleep, etc);  still have not found help online
  * brought the MBP to a Mac Genius
-- he ran some further tests, but found nothing;
-- he re-installed my OS as a hopeful-hail-mary-just-maybe-last-ditch effort; the problem persisted!
-- we both agreed that we had ruled out a software cause
-- he offered me to leave my MBP to get fixed for a flat fee of $300.00 (which after a couple weeks of trying to figure this out is starting to sound more and more reasonable)
Given that it is likely not a software issue, what hardware might it be? By booting from an OS on an external drive, I think I've ruled out a bad hard drive or hard drive cable. Also, given that inducing sleep in any way other than closing the MBP's lid does not cause the problem, it seems there might be a wire (or something) in the hinge section of the MBP that gets moved when the lid is closed possibly causing some kind of short circuit...or something.
If someone with more experience interpreting Console messages, for example, can help, I'd be happy to provide some logs, or any additional information.
Thank you for your time and consideration.

Answer 1

Ok, this is a crazy-simple, quasi-embarrassing fix, but I'll post it anyway just in case anyone is having a similar problem (for example, this guy: Changes to pmset being ignored).
Some time around late last August / early September (2014) this issue began happening for me (specifically, issue = closing lid while on battery power induces hibernation / shut down instead of sleep --- independent of hibernation mode). Maybe it was when I upgraded to Yosemite (not sure what the exact date of that was). As detailed in my original post, I frantically tried everything I could think of... At that time, however, I had quite a few presentations and posters to create and present at meetings and conferences, so I held off fixing it for a couple of months and returned to it this past week, where I tried a few more things listed above, but again to no avail...
This morning, I simply tried fudging around with all my power management settings again (via pmset in Terminal). The simplicity of the fix surprised me. But now that I understand it, I know it is likely the same fix for other threads I've read, such as the one above:
                                    (TLDR in bold)
(1) Take note of your power management settings (Terminal:  pmset -g custom)
(2) Is the "standby" flag set to 0? If so, set it to 1. Wa-la! Done.
This fix is crazy and embarrassing b/c I was so close to it for so long. I tried changing my hibernation modes multiple times (sudo pmset -a hibernatemode X, where X=0,1,3,25,etc). I read about manipulating other PMSET settings that helped other people with newer MBPs, like "autopoweroff" and "autopoweroffdelay" --- settings that I do not have on the MBP early 2011 (check your settings: pmset -g cap). And most amazingly of all, I even messed with the "standbydelay" setting, trying to make it so long that my computer should never go into hibernation... Yet, from what I can tell by looking over my notes, I never simply set "standby" from 0 to 1.
There are interesting questions that arise due to this fix. For example, why did this problem persist on clean installs of OS Yosemite? Is "standby" being set to 0 the Yosemite default? I'm not sure. If it is, then Kappy was right: this was normal behavior... It just wasn't always the normal behavior...at least not for my MBP. Normal behavior (hibernatemode 3) used to be (and now is again) that the MBP goes into safe sleep, and then only after an allotted amount of time will it go into full-blown hibernation.
NOTE: the "standby" and "standbydelay" PMSET settings are not available in some earlier MBP models (e.g., my brother has a 2010 and does not have these settings); so if you're having a similar problem with an earlier model, this fix might not be of any help to you.