Power Options for Tunneling Robots

Tunneling robots have many applications for instance laying underground cable, finding damaged pipelines, rescuing people from natural disasters, saving people from hostage situations or military applications in hunting down international terrorists at a time and place of our choosing. It is for this reason that the subject of tunneling robots came up recently in an online think tank. Which power option would you use so that the tunneling robot was powerful enough to complete its operations or mission?

One think tank member in discussing this stated;