Hi Colin,
An input from my experience with business continuance planning. Looked at solutions for High Availability, Site Redundancy, Geographical Redundancy, Disaster Recovery, etc.. As a part of this Power Supply, UPS, Battery, etc.. was a main item. Depending on the Site the Battery had 4 or 8 hours to run before they would be depleted. Mobile Power Generators were used to ensure sites could be charged.
VBR/ Wallis Dudhnath