The inventors have developed an ultra-stable reference electrode (RE) for energy storage and conversion systems for assessment of energy storage devices, including redox flow batteries. The reference electrode provides improved accuracy, stability, repeatability, and reliability when monitoring batteries. The electrode can be used in situ. More specifically, the newly invented RE, based on a dynamic hydrogen electrode (DHE) with a novel design on the area and surface roughness of platinum electrodes, demonstrates high accuracy and long-term stability that enables in-situ monitoring of individual electrode potentials throughout 500 cycles.