The weak spot is the battery backup system for the ONT. The battery needs to be replaced every-so-often. I've had to have the battery charging unit replaced multiple times over the years as they do eventually malfunction.
I read an article a while back - sorry I can't cite a reference offhand - that some phone company was repairing and re-certifying their copper infrastructure and just putting 48V battery on the pairs to power their fiber ONT's. Always on, no need to replace backup batteries, and no fixing blown out power supplies.
Makes sense. Every LEC just lashes their brand new fiber over the existing copper anyway, and it's already going to the same places. May as well use it for something.
