AbstractStretching a coiled carbon nanotube (CNT) yarn can provide large, reversible electrochemical capacitance changes, which convert mechanical energy to electricity. Here, it is shown that the performance of these “twistron” harvesters can be increased by optimizing the alignment of precursor CNT forests, plastically stretching the precursor twisted yarn, applying much higher tensile loads during precoiling twist than for coiling, using electrothermal pulse annealing under tension, and incorporating reduced graphene oxide nanoplates. The peak output power for a 1 and a 30 Hz sinusoidal deformation are 0.73 and 3.19 kW kg−1, respectively, which are 24‐ and 13‐fold that of previous twistron harvesters at these respective frequencies. This performance at 30 Hz is over 12‐fold that of other prior‐art mechanical energy harvesters for frequencies between 0.1 and 600 Hz. The maximum energy conversion efficiency is 7.2‐fold that for previous twistrons. Twistron anode and cathode yarn arrays are stretched 180° out‐of‐phase by locating them in the negative and positive compressibility directions of hinged wine‐rack frames, thereby doubling the output voltage and reducing the input mechanical energy.