Retina Macbook Pro doesn't hibernate
Since you did not post your pmset -g power profile, we can't be sure if it is set right.

First, autopoweroff specifically says it does not work if on battery power. Sure, that's dumb and contrary to common sense, but that's European power laws.

The correct setting is standby:

From 10.10.5's man page:


  STANDBY ARGUMENTS
  standby causes kernel power management to automatically hibernate a machine after it has slept for a specified time period. This saves power while asleep. This setting defaults to ON for supported hardware. The setting standby will be visible in pmset -g if the feature is supported on this machine.
  
  standby only works if hibernation is turned on to hibernatemode 3 or 25.
  
  standbydelay specifies the delay, in seconds, before writing the hibernation image to disk and powering off memory for Standby.


On my Macbook Pro, for some reason, it's:

Active Profiles:
Battery Power       -1*
AC Power        -1
Currently in use:
 standbydelay         4200
 standby              0
 halfdim              1
 sms                  1
 hibernatefile        /var/vm/sleepimage
 disksleep            10
 sleep                10
 hibernatemode        3
 ttyskeepawake        1
 displaysleep         3
 acwake               0
 lidwake              1


Notice Standby is set to 0. It should be changed to 1 to turn the feature on.

pmset -a standby 1