We have a fault light showing on our battery backup unit. From reading suggestions on here it suggests we plug in the power cable directly into the other unit. Could someone please advise what unit this is/what it looks like!
It’s the ONT, they vary a little but probably has LAN, LOS, PON & power LEDs. So you just unplug the power cable that goes from the BBU to the ONT & replace it with the power cable that goes into the BBU.
This shows the older 1+1 ONT/BBU enclosure , simply move the power lead from the BBU to the ONT , after removing the cable from the BBU to the ONT , the BBU was for the now defunct FVA ( fibre voice access ) phone port on this older style Huawei ONT
Your 4xAA Ni-MH rechargeable batteries in the BBU are shot.
Replace with like for like and you should be OK after they've fully charged.
unplug the power supply (DC in) at the BBU and plug it into the power port on the ONT.