Two types of electrochemical systems for harvesting energy from cyclic changes in environmental temperature using the thermogalvanic effect are demonstrated. Both systems are based on two battery stacks which function in either a dual-temperature or single-temperature configuration. In the dual-temperature configuration, two LiCoO2/Li cells were separately cycled between two temperatures to achieve an energy conversion with an efficiency of 0.22%, free of heat recuperation, and a peak output power of 0.4 μW when cycled between 20 °C and 50 °C. This energy conversion efficiency is comparable to other proposed systems for thermal energy harvesting such as charge-free thermally regenerative electrochemical cycle (TREC) devices, thermocapacitive devices and ionic thermoelectric supercapacitors. However, this system can function with a broader range of materials, which will likely allow further increases in efficiency and power. A single-temperature configuration in which two stacks of cells were cycled together between two temperatures was also demonstrated. Both systems are attractive for harvesting thermal energy for self-powered sensor networks, especially in remote areas.