Battery-powered Unmanned Aerial Vehicles are increasingly used to enhance humanitarian response. An ongoing initiative led by the World Food Programme is exploring their integration in response mechanisms, including last-mile relief distribution systems. Preliminary outcomes from this study are used to develop a relationship between payloads and energy consumption, considering vehicle endurance and other limitations. Building on this, we develop a non-linear trajectory optimisation model for battery-optimal flight paths. A bi-level location-routing heuristic is also developed, to determine the optimal location of supporting infrastructure in the distribution supply chain.