In this study, a novel polysiloxane-based gel agent (PSGA) was synthesized by using poly(dimethylsiloxane-co-alkylmethylsiloxane) and used as a gel agent for gel-valve-regulated lead-acid batteries. A PSGA was characterized by Fourier transform infrared, zeta meter, scanning electron microscopy, and energy-dispersive X-ray analysis. The electrochemical characterization of the gel system for the optimization of some parameters, such as concentration of gel agent, stirring rate, and agitation time, was conducted by cyclic voltammetric and electrochemical impedance spectroscopic analyses. The optimum concentration of the gel agent was determined as 6 wt% of the PSGA to form the best gel structure. The mechanical parameters related to the formation of a suitable gel structure were also investigated. The optimum stirring rate and agitation time were determined as 500 rpm and 2.5 h, respectively. The charge-discharge tests were applied to the gel system, and the highest capacity was determined in the PSGA-based gel system as 10 mAh at the end of the 100th cycle. The capacity of non-gelled system was the lowest.