Silver vanadium oxide (Ag2V4O11, SVO) has enjoyed widespread commercial success over the past 30 years as a cathode material for implantable cardiac defibrillator (ICD) batteries. Recently, silver vanadium phosphorous oxide (Ag2VO2PO4, SVPO) has been studied as possibly combining the desirable thermal stability aspects of LiFePO4 with the electrical conductivity of SVO. Further, due to the noted insoluble nature of most phosphate salts, a lower material solubility of SVPO relative to SVO is anticipated. Thus, the first vanadium dissolution studies of SVPO in battery electrolyte solutions are described herein. The equilibrium solubility of SVPO was ∼5 times less than SVO, with a rate constant of dissolution ∼3.5 times less than that of SVO. The vanadium dissolution in SVO and SVPO can be adequately described with a diffusion-layer model, as supported by the Noyes–Whitney equation. Cells prepared with vanadium-treated anodes displayed higher AC impedance and DC resistance relative to control anodes. These data support the premise that SVPO cells are likely to exhibit reduced cathode solubility and thus are less affected by increased cell resistance due to cathode solubility compared to SVO based cells.