I always considered using a UPS just in case of power failure, but never really got around to getting one. I once saw a guy at a tennis tournament use a small Honda generator, to power a Star 4.
I have to check the power supply, but I think it outputs 12V DC. Though I would not connect a battery directly to the tensioner unit.
Machines: Gamma 6004 2-point w/ Wise 2086 & Babolat Sensor Dual