As you probably know, some of the cellular sites are situated in the middle of nowhere. In that case there is no power line to be connected to. Typically in such cases you need to use diesel electrogenerator with some convertors to keep you cellular equipment working. Often you can spare, if you connect your remote site to any of "green" sources, like wind generator or solar panel. You probably can spare even more, if you will recharg emergency battery from wind/solar or their combo.
One of such systems from Ausonia you can find @ MWC2018 . Up to 24 kWt / 1600 Ah it is very compact. There are diesel generator inside, accumulators, DC/DC inventors and some smart controller, responsible for all the system.
As for the accumulators, now you can prefer to use modern Li Ion batteries instead of the lead-acid or lead-zink. Like that one from SAFT. Yes, you pay more, but you can expect even more in return. There are cylindrical Li-Ion cells inside with high rate charge & discharge capability and long cycle life.
There is another solution,more lightweight and powerfull - NiCad accumalators Tel-X. You choose!