Understanding structure/chemistry-function relationships of active battery materials is crucial for designing higher-performance batteries, with in situ synchrotron-based X-ray powder diffraction widely employed to gain this understanding. Such measurements cannot be performed using a conventional cell, with modifications necessary for the X-ray diffraction measurement, which unfortunately compromises battery performance and stability. Consequently, these measurements may not be representative of the typical behaviour of active materials in unmodified cells, particularly under more extreme operating conditions, such as at high voltage. Herein, we report a low-cost, simple, and robust coin-cell design enabling representative and typical cell performance during in situ X-ray powder diffraction measurements, which we demonstrate for the well-known high-voltage electrode material LiNi0.5Mn1.5O4. In addition to excellent cell stability at high voltage, the modified cell delivered an electrochemical response comparable to the standard 2032-type coin cell. This work paves an efficient way for battery researchers to perform high-quality in situ structural analysis with synchrotron X-ray radiation and will enable further insight into complex electrochemical processes in batteries.