The challenges facing metal-air batteries have prompted fundamental studies of non-aqueous electrochemistry. However it appears that contributors in the field are not aware that the potentials of Li/Li+, Na/Na+, K/K+, and Mg/Mg2+ electrodes depend on the nature of solvent due to the cation solvation. Therefore, it is imperative to define a clear potential scale that can be correlated in different solvents. Here we report on the strong effect of the solvent on the Li/Li+ redox potential and discuss the use of the ferrocene/ferrocenium couple as internal or external standard for the measurements in non-aqueous solvents in lithium-ion and lithium-02 battery systems. (C) The Author(s) 2017. Published by ECS. All rights reserved.