This is true also for fiber. Depending on the ISP fiber setup, the fiber can run for many 10's of km without a power relay.
I can run 1 Gbps symmetric for ~48h without power by running my optical network terminal (ONT) and a teeny travel router on battery packs. (Used this set up through several long power outages.)
I can run 1 Gbps symmetric for ~48h without power by running my optical network terminal (ONT) and a teeny travel router on battery packs. (Used this set up through several long power outages.)