With the importance of Li-ion and emerging alternative batteries to our electric future, predicting new sustainable materials, electrolytes, and complete cells that safely provide high performance, long life, and energy dense capability is critically important. Understanding the interface, the microstructure of materials, and the nature of electrolytes and factors that affect or limit long-term performance is key to new battery chemistries, cell form factors, and alternative materials. The electrochemical processes `that cause these changes are also difficult to probe because of their metastability and lifetimes, which can be of nanosecond to sub-nanosecond time domains. Consequently, developing and adapting high-resolution, nondestructive methods to capture these processes proves challenging, requiring state-of-the-art techniques. Recent progress is very promising, where optical spectroscopies, synchrotron radiation techniques, and energy-specific atom probe tomography and microscopy methods are just some of the approaches that are unraveling the true internal behavior of battery cells in real-time. In this review, we overview many of the most promising nondestructive methods developed in recent years to assess battery material properties, interfaces, processes, and reactions under operando conditions similar in electrodes and full cells.