Powder diffraction plays a central role in the characterization of light metal tetrahydroborates (borohydrides), novel boron based hydrides recognized as a potential solution for hydrogen storage. Numerous novel BH–4 based materials have been investigated during the past few years and this class of materials has a fascinating structural chemistry. We review the powder diffraction methods, problems and solutions which are specific for these weakly diffracting and badly crystallized materials. Examples of highlights and pitfalls of the powder diffraction are given. Complex structures with as many as 55 independent atoms were fully characterized, and P-T phase diagrams accessible from in-situ powder diffraction enable understanding of these ionic crystals with important directional bonding.