To avoid problems of cell towers not having power during a disaster, which happened during Katrina, when cell phone uses could call because there was no power. The FCC passed regulation to require carriers to have at least 8 hours of backup power available to cell towers.
A federal judge is looking at the matter and granted a stay to the regulation brought by Sprint Nextel. Arguments will be heard in the matter in May, the carrier don't want to pay for the cost increase.