Ultrathin galvanic cells that can comply with a variety of form factors and electronic system packages are of tremendous technological importance. They show promise for application in flexible electronic systems. This Thesis describes a flexible, high energy density galvanic cell, based on hydrated ruthenium (IV) oxide-zinc electrodes utilizing RuO2*nH2O nanoparticles in amounts that are not cost-prohibitive. This battery is suitable for use in a number of environments. It is non-toxic, environmentally friendly, and, based on aqueous electrolytes, it is safe in operation. It can be optimized for volume manufacture at low cost. As it functions at much lower cell voltage than Li-ion batteries, it can be recharged remotely, at conveniently low voltage, by harvesting, for example, radio-frequency (RF) energy. At present this cell demonstrates a specific capacity of over 50 mAh cm-2. This is the largest capacity reported for thin-film cells. Also, its cycle life of up to 200 charge-discharge cycles is very promising for use as a secondary galvanic cell. This Thesis focuses on (i) the optimization of anode and cathode materials, (ii) the identification of the composition of the electrolyte, (iii) the choice of the most suitable cell separator, and (iv) the elaboration of the most efficient assembly procedures.