With the growing popularity of 3G-powered devices, there are growing demands on energy-efficient data trans-mission strategies for various embedded systems. Different from the past work in energy-efficient real-time task scheduling, we explore strategies to maximize the amount of data transmitted by a 3G module under a given battery capacity. In particular, we present algorithms under different workload configurations with and without timing constraint considera-tions. Experiments were then conducted to verify the validity of the strategies and develop insights in energy-efficient data transmission.