Are you sure it's frequency fluctuations? If you are having constant frequency fluctuations, this may cause the UPS to go battery quite often and then eventually over-cycle the batteries until they are dead. I'd be interested to know how the UPS is failing (I'm the 9130 product manager!).
Are you having board failures? Other electrical issues are a more likely cause. Maybe frequency problems coupled with surges and harmonics? Rigs are notorious for filthy power.
