Nodes in wireless sensor networks (WSNs) are typically powered by batteries. Hence, their energy conservation is a critical problem. In this paper, pulse position modulation (PPM), one of the orthogonal signaling formats, is tailored for WSNs into two schemes: mono-mode PPM and multi-mode PPM. Resorting to an idealized system model and a practical system model, which combine the power consumptions in transmission and reception modules of nodes with the idealized and realistic battery characteristics, the energy efficiencies of mono- and multi-mode PPM are evaluated and compared. To minimize the battery energy consumption (BEC), these schemes are further optimized for a link in path-loss channels. Our analytical and numerical results show that considerable energy can be saved by multi-mode PPM, and/or by the parameter optimization in terms of constellation size M, at various communication distances.