If you are willing to mess with drivers, you may want to try installing Linux. On a 2013 Air, battery life and performance (even graphics!) are surprisingly better with Debian Jessie than with OS X. Of course, it is a newer model than yours, but the drivers will only be more stable and mature with a 2011. Especially if you have 4 GB RAM and you're running into a memory barrier with OS X, you should see a significant improvement.
Always 'Quit' open apps you don't use, never, NEVER have 2 sessions open at the same time, and try using lighter applications when you can (VLC instead of iTunes for music, Skim instead of Preview for PDFs, Preview instead of Photos for images, etc)
I have to use a 2012 MBP with Yosemite from time to time and if I follow these rules it is definitely bearable.
By the way, my battery health is also around 85% after 500 cycles and being plugged in and charged to 100% whenever possible.