Highkamp, it wasn't me but it seems easy to do. You need a buck converter, like this one I use:
www.adafruit.com/product/1385
and a 11.1V 5000mAh LIPO battery. Off the top of my head you should be able to get 2.5 hours out of a full charge assuming you draw down to 50% then stop, the Pi + USB devices draw 2A continuously, and the efficiency of the converter is 90%.
The challenge is what to do about the real energy hogs: dew heaters and TEC coolers. I use two 12V 35Ah deep-cycle batteries. They are light weight and won't break your back carrying around. I can go 6 hours powering a cooled camera, two Pi's, a RA stepper motor running continuously, dew heater, Flip Flat, Filter Wheel, and a 12V-to-19V boost converter to charge the laptop.