An off-board system for replacing electrolyte in a Metal-Air battery on board a vehicle, the off-board system comprising: a first tank for holding off-board electrolyte; a second tank for receiving and storing on-board electrolyte; an intermediate electrolyte tank for receiving on-board electrolyte; a waste electrolyte tank; fluid conduits to connect: the first tank, second tank and intermediate electrolyte tank to the battery; the intermediate electrolyte tank to the second tank; and the intermediate electrolyte tank to the waste electrolyte tank, sensors located in the intermediate electrolyte tank to measure a property of the on-board electrolyte; and a controller configured to replace the vehicle on-board electrolyte with an off-board electrolyte by: controlling transfer of the on-board electrolyte from the battery via the intermediate electrolyte tank to the waste tank or to the second tank based on a property of the electrolyte, measured by the sensors; controlling transfer of the on-board electrolyte from the intermediate electrolyte tank to the second tank when a property of the on-board electrolyte passes a threshold and to transfer the on-board electrolyte to the waste electrolyte tank otherwise; and to control transfer of off-board electrolyte from the first tank to the battery, wherein the property is at least one of: a chemical composition of the on-board electrolyte, a temperature of the on-board electrolyte, an amount of solid particles in the on-board electrolyte, a resistivity of the on-board electrolyte, a pH of the on-board electrolyte and the momentary amount of on-board electrolyte in the battery, each having a corresponding threshold value. a first tank for holding off-board electrolyte; a second tank for receiving and storing on-board electrolyte; an intermediate electrolyte tank for receiving on-board electrolyte; a waste electrolyte tank; fluid conduits to connect: the first tank, second tank and intermediate electrolyte tank to the battery; the intermediate electrolyte tank to the second tank; and the intermediate electrolyte tank to the waste electrolyte tank, the first tank, second tank and intermediate electrolyte tank to the battery; the intermediate electrolyte tank to the second tank; and the intermediate electrolyte tank to the waste electrolyte tank, sensors located in the intermediate electrolyte tank to measure a property of the on-board electrolyte; and a controller configured to replace the vehicle on-board electrolyte with an off-board electrolyte by: controlling transfer of the on-board electrolyte from the battery via the intermediate electrolyte tank to the waste tank or to the second tank based on a property of the electrolyte, measured by the sensors; controlling transfer of the on-board electrolyte from the intermediate electrolyte tank to the second tank when a property of the on-board electrolyte passes a threshold and to transfer the on-board electrolyte to the waste electrolyte tank otherwise; and to control transfer of off-board electrolyte from the first tank to the battery, wherein the property is at least one of: a chemical composition of the on-board electrolyte, a temperature of the on-board electrolyte, an amount of solid particles in the on-board electrolyte, a resistivity of the on-board electrolyte, a pH of the on-board electrolyte and the momentary amount of on-board electrolyte in the battery, each having a corresponding threshold value. controlling transfer of the on-board electrolyte from the battery via the intermediate electrolyte tank to the waste tank or to the second tank based on a property of the electrolyte, measured by the sensors; controlling transfer of the on-board electrolyte from the intermediate electrolyte tank to the second tank when a property of the on-board electrolyte passes a threshold and to transfer the on-board electrolyte to the waste electrolyte tank otherwise; and to control transfer of off-board electrolyte from the first tank to the battery, wherein the property is at least one of: a chemical composition of the on-board electrolyte, a temperature of the on-board electrolyte, an amount of solid particles in the on-board electrolyte, a resistivity of the on-board electrolyte, a pH of the on-board electrolyte and the momentary amount of on-board electrolyte in the battery, each having a corresponding threshold value.