Aqueous organic redox flow batteries (AORFBs) have received increasing attention as an emergent battery technology for grid-scale renewable energy storage. However, physicochemical properties of redox-active organic electrolytes remain fine refinement to maximize their performance in RFBs. Herein, we report a carboxylate functionalized viologen derivative, N, N'-dibutyrate-4,4'-bipyridinium,(CBu)2V, as a highly stable, high capacity anolyte material under near pH neutral conditions.(CBu)2Vcan achieve more than 2.1 M solubility and display a reversible, kinetically fast reduction at -0.43 V vs NHE at pH 9.DFT studies revealed that the high solubility of(CBu)2Vis attributed to its high molecular polarity while its negative reduction potential is benefitted from electron-donating carboxylate groups. A 0.89 V (CBu)2V/(NH)4Fe(CN)6AORFB demonstrated exceptional energy storage performance, specifically, 100% capacity retention with a utilized energy density of 9.5 Wh/L for 1000 cycles, power densities of up to 85 mW/cm2, and an energy efficiency of 70% at 60 mA/cm2.(CBu)2Vnot only represents the most capacity dense viologen with pendant ionic groups and also exhibits the longest (1200 hours or 50 days), most stable flow battery performance to date.