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Batteries and fuel cells have already shown high potential across a diverse range of applications such as automotive power trains, space propulsion and medical implants. However, further developments are still required with regards to reliability, efficiency and safety. For that, multimodal and complementary characterisation methods that combine common investigation tools may allow one technique, e.g. X-ray, to overcome the drawbacks of another, e.g. neutron, and vice versa. For instance, recent developments in innovative neutron imaging techniques, which is highly sensitive to lithium and hydrogen, are able to compliment X-ray methods that cannot easily detect such light elements, closing the gaps in information. This thesis utilises the latest neutron and X-ray techniques to examine commercial and lab-made lithium metal, Li-ion battery and fuel cells. Four-dimensional (4D) high-resolved neutron and X-ray computed tomography (CT) allow the quantitative determination of the lithium transport inside commercial Li/SOCl2 cells, and the detection of the electrolyte consumption and degradation processes which affect the cell capacity. High throughput X-ray CT has enabled the identification of mechanical degradation processes in commercial Li/MnO2 Li-ion primary batteries. Complementary neutron CT has identified the lithium diffusion process and electrode wetting by electrolyte. Virtual electrode unrolling techniques provide a deeper view inside the electrode layers and detect minor fluctuations which are difficult to observe using conventional three-dimensional (3D) rendering tools. High-speed operando CT has shown temporal resolved water evolution in the electrode flow-fields and the membrane electrode assembly of polymer electrolyte fuel cells in 3D for the first time. This allow a quantitative comparison between different operation modes and cell designs by the water management. 4D neutron Bragg edge imaging has shown their potential to characterise the different lithiation phases spatially resolved in novel directional ice templated graphite electrodes. Finally, 3D Bragg Ptychography is utilised to visualise the nano-metre layered crystal structure of small graphite flakes used as active electrode material in Li-ion batteries.