The performances of rechargeable Li-based batteries depend on many factors amongst which is the structural evolution of the electrode materials upon cycling. To address these issues, efforts have been devoted towards reliable, rapid, and facile ways to perform in situ measurements. We show how recent advances in both cell design (e.g. the emergence of plastic cells) and instrumentation have boosted the implementation of in situ X-ray characterisation methods to the field of energy storage. The benefits of such measurements are discussed and commented through descriptive examples of a new insertion electrode material (PNb9O25) and an existing one of commercial interest LiCoO2. The link between the fundamental findings and their relevance to practical applications is highlighted. The rapidly growing field of in situ characterisation techniques in the field of battery materials extending beyond X-rays and involving XANES, Mossbauer, Raman, RMN and microscopy measurements, is also commented on.