In situ and operando techniques play an important role in modern battery materials research and development. As materials characterization and application requirements advance, so too must the in situ/operando test methods and hardware. The effects of temperature, internal mechanical pressure and parasitic reactions due to, for example, cell sealing are critical for commercial scale-up but often overlooked in in situ/operando cell designs. An improved electrochemical operando cell for X-ray diffraction and spectroscopy using ConFlat-style flanges in combination with a beryllium window is presented. The cell is reusable and simple to fabricate and assemble, providing superior sealing, relevant and adjustable cell stack pressure, and reproducible charge/discharge cycling performance for short- and long-term experiments. Cell construction, electrochemical performance, and representative operando X-ray powder diffraction measurements with carbon and aluminium electrodes at temperatures between 303 and 393 K are provided. Operando electrochemical cell testing at high temperatures allows access to temperature-sensitive phase transitions and opens the way for analysis and development of new lithium-based cathode, anode and electrolyte materials for lithium-ion batteries.