Peeking inside batteries while the devices are being charged or discharged could lead to electrochemical insights that enable researchers to design safer and longer-lasting batteries. But getting an up-close view of a working battery has been notoriously difficult. Scientists may now be able to get such a view by using a 7Li magnetic resonance imaging (MRI) technique developed by Srinivasan Chandrashekar and Alexej Jerschow of New York University; Clare P. Grey of Cambridge University and the State University of New York, Stony Brook; and coworkers (Nat. Mater., DOI: 10.1038/nmat3246). The method provides a noninvasive way to visually monitor changes in battery components that have traditionally been inaccessible to diagnostic methods. The team showed that MRI can reveal the existence of lithium deposits (dendrites) that grow and extend into the region between electrodes when a test cell is charged. Buildup of such microstructures has been identified as a key factor triggering short circuits in lithium batteries. The team notes that the method can be used to monitor other types of undesirable lithium deposits, the techniques for dispersing them, and their dependence on charge rates, discharge rates, and other battery parameters.