© Copyright 2017 Materials Research Society. The stability of vanadium flow battery (VFB) catholytes was investigated using both lightscattering measurements and visual observation. V2O5 precipitates after an induction time ¿ which shows an Arrhenius variation with temperature. The value of ¿ increases with increasing concentration of sulfate and with decreasing concentration of VVbut the activation energy remains constant with a value of (1.791±0.020) eV. Plots of ln ¿ against [S] and [VV] show good linearity and the slopes give values of ßS= 2.073 M-1and ßV5= -3.434 M-1for the fractional rates of variation of ¿ with [S] and [VV], respectively. Combining the Arrhenius Equation with the observed log-linear variation of ¿ with [S] and [VV] provides a model for simulating the stability of catholytes.