Telecom towers and their power

Thanks. My family is OK, but I imagine they are not used to being without power or phone service. I was more wondering about the tellycom towers and if there are standards for how long they have to be able to run when the grid goes down.
We talk about telecom batteries on this forum a bit, I was just wondering how long major towers can rely on battery power alone and the same about generators and if anybody here was familiar with the size of their battery banks and how long they can power a cell phone tower.