Optical Network Terminal
The install didn't go as i had wanted.
1. The ONT is a Huawei HG8010H5-20, not a Nokia as i wanted, more on that in the comments.
2. The engineer had trouble connecting the fibre to the connector and used a CSP and sadly a large outdoor version was all he had, more on that two.
3. After set up all was fine, running both temporarily from 230v ac.
Rewired router and ONT to 12v via a switch on the 12v distribution mash.
The ONT is using 150mA, so at a nominal 12v that's 1.8w, more like 2w as V=13
ONT was fine on 15.88V whilst the battery was on equalisation.
Tidying could be done a) the dc power cable can be shortened and b) may find a short (32cm) ethernet cable