Unmanned　aerial　vehicles　(UAVs)　may　be　used　for　providing　seamless　network　coverage　in　urban　areas　for　improving　the　performance　of　conventional　cellular　networks.　Given　the　predominantly　line-of-sight　channel　of　drones,　UAV-aided　seamless　coverage　becomes　particularly　beneficial　in　case　of　emergency　situations.　However,　a　single　UAV　having　a　limited　cruising　capability　is　unable　to　provide　seamless　long-term　coverage,　multiple　drones　relying　on　sophisticated　recharging　and　reshuffling　schemes　are　necessary.　In　this　context,　both　the　positioning　and　the　flight　strategy　directly　affect　the　efficiency　of　the　system.　Hence,　we　first　introduce　a　novel　UAV　energy　consumption　model,　based　on　which　an　energy-efficiency-based　objective　function　is　derived.　Second,　we　propose　an　energy-efficient　rechargeable　UAV　deployment　strategy　optimized　under　a　seamless　coverage　constraint.　Explicitly,　a　two-stage　joint　optimization　algorithm　is　conceived　for　solving　both　the　optimal　UAV　deployment　and　the　cyclic　UAV　recharging　and　reshuffling　strategy.　Our　simulation　results　quantify　the　efficiency　of　our　proposed　algorithm.