In any large telecoms company facility or Data centre operator the UPS is not just a simple back up system . It does what it saysd , it is an uninteruptable power supply and it sits between things like diverse mains inlets and on site generators. It manages the switch from one to other if required and very importantly smooths out or buffers any spikes which are common on any electrical system underload if it is suddenly interrupted or switched. So that s like one per BT exchange and goodness knows what for a BT Network Ops centre or even a modest data centre.
Havign worked in that industry power problems are not unknown but you have to protect against them in every possible way at critical facilities. That said we ahd management who would come up with idiotic comments like , its not going to produce any more revenue can you delay replacing for 2 years and two years later a different genius asks the same question.
This is an almighty cock up on BAs part and there are huge incentives for the management to be evasive about what happened especially as there wont be any independent investigators.