An external battery bank is another kettle of fish altogether from the OP's question about dash cams that "operate just using a built in battery", but yes, you can get extremely long battery operated run-times that way. It doesn't need to be a Mobius. Recently, I ran some tests running an SG9665GC (about 1/2 amp draw) using two different (not brand new) 20,000mAh power banks and was able to run the cam continuously for between 44.5 and 52 hours .