This link claims that Apple upped the default resolution being scaled for the Retina display and that if you set it back to the prior setting, you'll get more battery life. (Also if your are older you'll just be able to read it again.)
I was actually kind of shocked to read about this change. Usually Apple increases resolution but finds a way to keep all the proportions all the same. In this case everything on the screen just got smaller.
Anyway per the link it activates the dGPU less and you get an extra 45-50 minutes per charge. That doesn't suck.