In the past two decades’ significant studies have been reported on electrically conducting thermoplastic composites of acrylonitrile butadiene styrene (ABS), polyvinylidene fluoride (PVDF), etc. for the fabrication of novel energy storage devices (ESD) by 3D printing. But hitherto little has been reported on onlinecondition monitoring of ESD prepared by secondary (2°) recycling of ABS. This study reports the investigations on mechanical and electrical properties of NH₄Cl–ZnCl₂ (electrolyte) reinforced ABS composite (as 3D printed sensor) for online condition monitoring of ESD. In a typical dry cell, the electrolyte is one of the integral parts, and the change in its dielectric properties with the time/ applied electric load has been used to ascertain the health of ESD (online) as the internet of things (IoT) based solution (Bluetooth application) in industry sportsand medicine (ISM) band (2.4 GHz). Based on melt flow index (MFI), 10% NH₄Cl and 10% ZnCl₂ (by weight%) were reinforced in ABS for preparing 3D printed rectangular substrates as ring resonators for calculating dielectric constant (εr) and loss tangent/dissipation factor (tanδ) for the resonant frequency. Transmission line parameters (S₂₁) were observed using a vector network analyzer (VNA), and a high-frequency structure simulation (HFSS) software package. The results are supported by morphological analysis of ABScomposite based on scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), 3D rendering, surface roughness (R_a), area mapping, current (I)–voltage (V), and Fourier transformed infrared (FTIR) characterization.