The battery backup will run the whole cabinet, apparently for a minimum of 4 hours

Bob will know better

When we had a 36 hour power failure recently - fire in substation - VirginMedia did the rounds of their cabinets with a small Honda generator topping up the batteries until United Utilities connected a monster generator on a truck at the substation..
AFAIK VirginMedia have no copper path back to the exchange.

They have no copper back to the exchange as VM don't have exchanges.

"It is powerered from the exchange which will have at least a few hours bateery back up enabling engineersd to fix the power issue "

No, the exchanges have their own diesel powered generators.

/me whispers in Bob_s2's ear

with electric starter motors.

Very few exhchanges have generator sets nowadays. The batteries should keep the exchange going for several hours untill the can fix the power fault or move in aa mobile generator. Another last ressort is each subscriber wil have a class of service so they can use that to conserve the batteries. Ordinary subscribers would get cut of first then businesses and less critical users such as OAP homes etc

Since System X & AXE10 exchanges came in (years ago), I haven't seen an exchange without a standby generator.

ROFL, you do like to spout bovine dung to people who know.

The first bit is wrong, but you take the biscuit with .....

"Another last ressort is each subscriber wil have a class of service so they can use that to conserve the batteries. Ordinary subscribers would get cut of first then businesses and less critical users such as OAP homes etc"

Utter tosh.