<p>Stack pressure is essential for ensuring solid–solid interfacial contact in batteries, where it plays a particularly crucial role. The wide variation in stack pressure levels in batteries has perplexed researchers seeking to determine an optimal value and has led to substantial gaps in our understanding of how stack pressure interacts with battery chemistry. Here we highlight the critical importance of stack pressure in batteries and advocate for considering a critical stack pressure empirical model as a means to determine the optimal stack pressure. We begin by analysing the broad range of stack pressures, which span multiple orders of magnitude. We then categorize their effects into four distinct stages and explain their roles. Additionally, we examine the electrochemomechanical relationship of stack pressure to reveal a coupled effect. Future research on stack pressure should focus on areas such as benchmarking, diagnosis, spatial distribution and minimization. A deeper understanding of stack pressure will facilitate the development of more reliable and practical battery designs across various chemistries.</p>