-
FTTP is powered by electricity at the exchange and in the local cabinet so any loss of local area electricity and that will drop out. 4g likely to go the same way if the power drops in your local area (happened to me recently)
The question is, what are you hoping to protect against with this battery? a home power loss (distribution board packing up) or loss of the local area supply.
There’s no BT line, not sure about how the FTTH is powered. Could always add a 4G dongle to the AP, still would need power to another AP at another location (which is the wfh office - granted that could also be a larger power station that way I could also power the displays…)
I agree adding tado to the list above was not necessary :-) House batt and solar would be 20-50 times more expensive than what I have in mind, plus might have to deal with bad workmanship.