In situ characterization plays a crucial role in unveiling the mechanisms of batteries under operation conditions. Nuclear Magnetic Resonance (NMR) can effectively serve as a non-invasive approach to capture the evolution of electrodes and electrolyte upon electrochemical cycling. The insights into metaphase formation, self-diffusion, kinetics and inhomogeneity that are obtained along temporal and spatial dimensions from in situ NMR/MRI can serve as a guide for the structural design and modification of materials, and for the fabrication of batteries with optimized performance. This chapter focuses on the applications of in situ NMR/MRI for the energy storage community. In particular, some examples of ¹H, ⁷Li, ²³Na and ³¹P in situ NMR applications in different electrodes as well as in situ MRI on electrolytes and electrodes with or without chemical shift information (CSI, S-ISIS, and stray-field MRI) are presented. Furthermore, in situ NMR applied to other energy systems is briefly summarized, and finally the limitations and perspectives of in situ NMR/MRI for working batteries are discussed.