I am sure the topic of RPi power has been exhausted but I just discovered a new warning/something-to-gripe-about:

Recently I purchased a 12V battery power distribution panel from a reputable firm. The panel has the usual 12V fused PowerPole connector outputs. Also it has two 5V regulated USB-A outputs. How nice is that? Now I can power my two Raspberry Pi's. I tested the no-load voltage out of one of the ports and it was a cool 5.02V. Wow, I thought, they must be using one helluva good regulator. Well, it turned out that the stinking thing drops to 4.6V at 0.5A load. The Pi will actually complain about under-voltage when you hook up a monitor. I didn't do that. I ran it headless. After just a couple nights of imaging the VAP dropped out. I tried a proper PSU to no avail. I tired re-flashing the SD card -- nope.

I recommend getting something like a "Charge Doctor" from Adafruit:
www.adafruit.com/product/1852

Test your power supply before harming your Pi. Under no load it should read 5.2V +/- 0.05V. If it doesn't then keep it away from your Pi.

I use one of these 12v to 5v regulators, connected to my Pegasus Ultimate power hub, works like a charm...

Yes, got two of those but was hoping that West Mountain Radio of Waukesha, WI could do equally well -- apparently not. No word yet on how they are going to remedy the problem.

Kamisan, I recall reading a post about someone powering their two Rpi with Li battery pack. Was that you and if so which ones do you use?

Thanks

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.