Disclosed is a method for preparing a 
high energy density (HED) 
electrolyte solution for use in an all-
vanadium redox cells, a 
high energy density 
electrolyte solution, in particular an all-
vanadium high energy density 
electrolyte solution, a 
redox cell, in particular an all-
vanadium redox cell, comprising the high 
energy density electrolyte solution, a redox battery, in particular an all-
vanadium redox battery, comprising the HED electrolyte solution, a process for recharging a discharged or partially discharged redox battery, in particular an all-
vanadium redox battery, comprising the HED electrolyte solution, a process for the production of 
electricity from a charged redox battery, and in particular a charged all-
vanadium redox battery, comprising the HED electrolyte, a redox battery / fuel 
cell and a process for the production of 
electricity from a redox battery / fuel cell. A method for stabilising an electrolyte solution for use in a redox cell, in particular for stabilising an electrolyte solution for use in an all-vanadium redox cell, a stabilised electrolyte solution, in particular an all-vanadium stabilised electrolyte solution, a redox cell, in particular an all-vanadium redox cell, comprising the stabilised electrolyte solution, a redox battery, in particular an all-vanadium redox battery comprising the stabilised electrolyte solution, a process for recharging a discharged or partially discharged redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte solution, and a process for the production of 
electricity from a charged redox battery, and in particular a charged all-vanadium redox battery, comprising the stabilised electrolyte solution are disclosed. Also disclosed are a redox battery / fuel cell and a process for the production of electricity from a redox battery / fuel cell.