Many mobile applications rely on location information gained from location services on mobile devices. However, continuously tracking the device location with high accuracy drains the battery quickly. Furthermore, sensing the same location can be redundant when multiple devices are co-located. In this paper, we develop a crowdsourcing-based location service, E2A2 (energy efficient and accuracy aware), which places colo-cated devices into groups, and uses group location to represent individual device location. The E2A2 location service aims to reduce individual device battery consumption associated with location services while simultaneously maintaining high location accuracy for each device. Our experimental results from a prototype system show the effectiveness of our proposed solution with different mobility patterns. We also present results on the impact of different system parameters and the number of users in a group. Compared to running GPS location services on individual devices separately, our E2A2 service saves on average 33% battery consumption rate when 4 devices are co-located at walking speed and 26% battery consumption rate when 4 devices are colocated on the same bus while meeting the same accuracy requirements.