This study addresses the critical challenge of maintaining uniform and accurate control of cycling pressure in all-solid-state batteries (ASSBs) to ensure effective interfacial contacts between materials. Traditional uniaxial cell holders used in battery research struggle to accommodate electrode volume changes, provide uniform pressure distribution, and maintain consistent pressure over time. The authors introduce isostatic pouch cell holders (IPCHs) that use air as the pressurizing medium to achieve uniform and regulated cycling pressure. LiNi0.8Co0.1Mn0.1O2 | Li6PS5Cl | Si pouch cells were fabricated and tested under pressures ranging from 1 to 5 MPa, showing improved electrochemical performance with higher cycling pressures, with 2 MPa being 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 findings highlight the effectiveness of IPCHs in enhancing the performance and practical application of ASSBs. The study also discusses the advantages of IPCHs over uniaxial cell holders, including better pressure uniformity, resistance to material fatigue, and the ability to accommodate multiple cells in a stack, leading to higher energy density and reduced module weight.This study addresses the critical challenge of maintaining uniform and accurate control of cycling pressure in all-solid-state batteries (ASSBs) to ensure effective interfacial contacts between materials. Traditional uniaxial cell holders used in battery research struggle to accommodate electrode volume changes, provide uniform pressure distribution, and maintain consistent pressure over time. The authors introduce isostatic pouch cell holders (IPCHs) that use air as the pressurizing medium to achieve uniform and regulated cycling pressure. LiNi0.8Co0.1Mn0.1O2 | Li6PS5Cl | Si pouch cells were fabricated and tested under pressures ranging from 1 to 5 MPa, showing improved electrochemical performance with higher cycling pressures, with 2 MPa being 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 findings highlight the effectiveness of IPCHs in enhancing the performance and practical application of ASSBs. The study also discusses the advantages of IPCHs over uniaxial cell holders, including better pressure uniformity, resistance to material fatigue, and the ability to accommodate multiple cells in a stack, leading to higher energy density and reduced module weight.