An in-situ method for measuring the variation of battery stack thickness employing a linear voltage displacement transducer device is described. Prismatic lithium ion batteries based on the cathode active materials LiMn2O4 and LiCoO2 are investigated. These batteries comprise multiple, parallel-connected bi-cells. The manganese system reveals only minor thickness variations during a single low rate, charge-discharge cycle. The maximum thickness change for the approximate 9 mm stack amounted to only 20 mu m corresponding to less than a 0.2% overall variation. We determine that the battery stack is at its thickest at around 45% state of charge and at its thinnest in the fully discharged state. For the cobalt battery, more significant thickness variations are determined. This behavior is consistent with the concurrent expansion of both the anode and cathode lattices during the battery charging process. The thickness changes are shown to be reversible within a single charge-discharge cycle. As a function of battery state-of-charge, the dimensional variations were clearly demonstrated to be non-linear. The cobalt oxide battery stack was at its thickest when fully charged and at its thinnest when fully discharged. At the fully charged condition the 8.8 mm prismatic stack was shown to increase in thickness lover the fully discharge case) by about 140 mu m stack representing a 1.6% overall expansion.