Next job is replacing the NBN NTD backup battery. These are designed to be user replaceable and it is easy to do. From what I’ve heard, the charging circuit in these is not good so the batteries don’t last as long as they should and I don’t think NBN supply the battery backup units by default anymore but they do keep the NTD powered for several hours if power is lost so it is worth replacing the battery. 
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Discussion
Yeah NBN don’t provide batteries anymore unless you have a medical condition and need a more reliable phone line. Have you ever used NBN in a power outage? I’ve always been curious whether the exchanges / nodes in the street have battery backup to maintain the fibre connection.
I’ve used mine during short power outages with no issues. How long the NBN side equipment will run for during a power outage will depend on which technology is used. For FTTP everything is passive between the house and the OLT in the NBN POI. The NBN POIs generally have large battery backups and generators so can run for a long time.
For FTTN, there is a VDSL DSLAM in the street cabinets that requires power and I believe they have some battery backup but I’m not sure for how long.
FTTC uses a small DSLAM in the pit outside of the house (1 shares between 4 houses) and these are reverse powered from the house so if the house still has power (e.g. the NTD is on a UPS) then I believe they will keep on working.
I don’t know much about how the HFC network is built but I think there is active equipment in the streets that has limited battery backup.
That’s good to know, it’s a bit of a mine field with all of the different NBN connections. I had HFC at an old house I lived at but never tested it under power outage (didn’t have the HFC box connected via battery back-up anyway).