I'm running an external battery test right now, line in with zero added gain at DSD resolution (what's the practical difference between the three DSD formats they let you choose, but don't talk about at all?). SO far it's gone 3 3/4 hours with the guage on the Powerstick 15 (a BatteryGeek Lithium Ion adjustable voltage battery/small flashlight) showing about 1/2 charge still remaining in the Powerstick and full battery in the MR-1. The Powerstick is about the same height and thickness as the MR-1, about 1/2 as wide, weighs a little over 6 oz. It is rated at 4000mAh (but I think you have to run it at 3.7V to get that, it is 14.8 Wh rated, which would be about 3000 mAh at 5V). This looks viable.
Jeff