<![CDATA[Flexible strain sensors hold great potential for applications in wearable electronic devices, human motion monitoring, and rehabilitation systems. However, the development of such sensors still faces challenges in producing conductive networks that are both sensitive and stable while reducing reliance on commercial conductive materials. This study developed an Ecoflex/MWCNT–RBC-based flexible strain sensor (FSS) by utilizing recycled battery carbon (RBC) obtained from carbon rods in zinc–carbon battery waste. The RBC was separated, washed, dried, crushed, and sieved into a powder, then mixed with multi-walled carbon nanotubes (MWCNT) in isopropyl alcohol using ultrasonic homogenization. The mixture was applied to a pre-cured Ecoflex layer, fitted with copper electrodes, and encapsulated using an Ecoflex layer to produce a layered sensor structure. The morphology and conductive network of the sensor were analyzed using SEM, while its electromechanical performance was evaluated through testing of sensitivity, linearity, cyclic response, response and recovery times, and durability. The sensor produced a measurement factor of 15.42 over a strain range of 0–100%, with a linearity (R²) of 0.994. Response and recovery times were recorded at 70 ms and 70 ms, respectively, while the sensor’s stability was maintained for up to 500 load–unload cycles at 80% strain. These results demonstrate that RBC can serve as a secondary conductive material alongside MWCNT in producing flexible, responsive, and stable strain sensors. This approach offers a sustainable strategy for converting carbon from battery waste into value-added functional materials for wearable sensor applications.]]>
