A comprehensive examination of the requirements and current state-of-the-art of electrolytes and electrodes for calcium batteries is presented, flowing from past attempts to develop (rechargeable) technologies via crucial breakthroughs to arrive at a comprehensive discussion of the current challenges at hand. Advantages being sustainability (calcium is the fifth most abundant element in the earth crust) and the potential to deliver high energy density, the realization of a rechargeable Ca battery technology primarily requires identification and development of suitable electrodes and electrolytes.  The progress starting from the fundamental electrode/electrolyte requirements, concepts, materials, and compositions employed is discussed and a critical analysis of the state-of-the-art allows to conclude with the particular roadblocks still exist. As for crucial breakthroughs reversible plating and stripping of calcium at the metal anode interface was achieved only recently and for very specific electrolyte formulations. Therefore, while much of current research aims at finding suitable cathodes to achieve proof-of-concept for a full Ca battery, the spectrum of electrolytes researched is also being gradually expanded. Assessing compatibility of cell components is essential.  To that end, proper characterization is needed, which requires design of a multitude of reliable experimental set-ups and sometimes methodology development beyond that of other next generation battery technologies, as know how gained in the field of Li-ion cannot be blindly adopted.

Strategies to make best use of the current advances in materials science combined with computational design, electrochemistry and battery engineering should serve to propel the Ca battery technology to reality and ultimately reach its full potential for energy storage.