Abstract: A state of charge indicator arrangement for a redox flow battery system having a reference cell arrangement for measuring potential difference between positive electrolyte and negative electrolytes and an auxiliary reference electrolyte arrangement comprising a discrete auxiliary electrolyte reservoir for housing a redox electrode in association with a reference electrolyte, a means of measuring the potential difference between the auxiliary reference electrolyte and the electrolyte of the reference cell arrangement and an ionic pathway conduit linking the auxiliary reference electrolyte reservoir with the electrolyte of the reference cell arrangement, which is configured for low fluid diffusion rate, wherein the conduit comprises a wicking means for absorbing electrolyte and maintaining ionic connection between the auxiliary reference electrolyte reservoir and the respective electrolyte of the reference cell arrangement.

Abstract: A state of charge indicator arrangement for a redox flow battery system having a reference cell arrangement for measuring potential difference between a positive electrolyte and a negative electrolyte of the flow battery and an auxiliary reference electrolyte arrangement is provided. The indicator includes a discrete auxiliary electrolyte reservoir for housing a redox electrode in association with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte for which it provides a reference, a means of measuring the potential difference between the auxiliary reference electrolyte and the electrolyte of the reference cell arrangement and an ionic pathway conduit linking the auxiliary reference electrolyte reservoir with the electrolyte of the reference cell arrangement, which is configured for low fluid diffusion rate.