This study introduces isostatic pouch cell holders to enable uniform and accurate cycling pressure control for all-solid-state batteries (ASSBs), addressing the challenges of maintaining effective interfacial contacts between materials. Traditional uniaxial cell holders struggle with electrode volume changes, uneven pressure distribution, and consistent pressure over time. The proposed isostatic pouch cell holder (IPCH) uses air as a pressurizing medium to achieve uniform and regulated cycling pressure. The research fabricated and tested LiNi0.8Co0.1Mn0.1O2 | Li6PS5Cl | Si pouch cells under 1–5 MPa pressures, revealing improved electrochemical performance with higher cycling pressures, with 2 MPa as the minimum for optimal operation. A bilayer pouch cell with a theoretical capacity of 100 mAh demonstrated a first-cycle Coulombic efficiency of 76.9% and a discharge capacity of 173.6 mAh g−1 (88.1 mAh), maintaining 83.6% capacity after 100 cycles. These results highlight the effectiveness of IPCHs in enhancing ASSB performance and practical application. The study emphasizes the importance of uniform cycling pressure for maintaining intimate interfacial contact and ensuring ASSB performance during both fabrication and cycling. IPCHs offer advantages over traditional uniaxial holders by providing more uniform pressure distribution, reducing structural fatigue, and accommodating electrode volume changes. The IPCH design uses a chamber and gaskets to contain pressurized fluid, allowing for stable pressure regulation even under temperature fluctuations. The research also evaluated the electrochemical performance of ASSBs under different cycling pressures, showing that lower pressures can lead to reduced Coulombic efficiency and faster capacity fade due to increased unwanted surface reactions and delamination. The study demonstrated that higher cycling pressures support better interfacial contact, leading to improved electrochemical performance. The IPCH design was tested with various cell formats, including a bilayer ASSPC, which showed practical capacity of approximately 88.1 mAh at 0.1 C for 50 cycles and the ability to discharge at 3 C, powering an incandescent light bulb. The study concludes that isostatic pressurization provides a uniform and accurate method for studying pressure effects on ASSPCs and contributes to the commercialization of ASSBs. The IPCH design is more efficient and practical for real-world applications, offering higher energy density and better performance compared to traditional methods.This study introduces isostatic pouch cell holders to enable uniform and accurate cycling pressure control for all-solid-state batteries (ASSBs), addressing the challenges of maintaining effective interfacial contacts between materials. Traditional uniaxial cell holders struggle with electrode volume changes, uneven pressure distribution, and consistent pressure over time. The proposed isostatic pouch cell holder (IPCH) uses air as a pressurizing medium to achieve uniform and regulated cycling pressure. The research fabricated and tested LiNi0.8Co0.1Mn0.1O2 | Li6PS5Cl | Si pouch cells under 1–5 MPa pressures, revealing improved electrochemical performance with higher cycling pressures, with 2 MPa as the minimum for optimal operation. A bilayer pouch cell with a theoretical capacity of 100 mAh demonstrated a first-cycle Coulombic efficiency of 76.9% and a discharge capacity of 173.6 mAh g−1 (88.1 mAh), maintaining 83.6% capacity after 100 cycles. These results highlight the effectiveness of IPCHs in enhancing ASSB performance and practical application. The study emphasizes the importance of uniform cycling pressure for maintaining intimate interfacial contact and ensuring ASSB performance during both fabrication and cycling. IPCHs offer advantages over traditional uniaxial holders by providing more uniform pressure distribution, reducing structural fatigue, and accommodating electrode volume changes. The IPCH design uses a chamber and gaskets to contain pressurized fluid, allowing for stable pressure regulation even under temperature fluctuations. The research also evaluated the electrochemical performance of ASSBs under different cycling pressures, showing that lower pressures can lead to reduced Coulombic efficiency and faster capacity fade due to increased unwanted surface reactions and delamination. The study demonstrated that higher cycling pressures support better interfacial contact, leading to improved electrochemical performance. The IPCH design was tested with various cell formats, including a bilayer ASSPC, which showed practical capacity of approximately 88.1 mAh at 0.1 C for 50 cycles and the ability to discharge at 3 C, powering an incandescent light bulb. The study concludes that isostatic pressurization provides a uniform and accurate method for studying pressure effects on ASSPCs and contributes to the commercialization of ASSBs. The IPCH design is more efficient and practical for real-world applications, offering higher energy density and better performance compared to traditional methods.