A method for sensing the electrolytic conductivity of a fluid, the method comprising: - providing a battery comprising an oxidizing electrode and a reducing electrode separated at a distance and connected by a hydrophilic and/or a porous material or an empty receptacle providing a microfluidic cavity, wherein the battery is sensitive, only, to the presence of analytes with ionic charge that determine an electrolytic conductivity of a fluid to be sensed, the fluid acting as battery electrolyte and not as a fuel, wherein the oxidizing and reducing electrodes are connected through the fluid , wherein an internal resistance of the battery depends on said electrolytic conductivity of the fluid , and wherein the battery is activated upon the addition of said fluid to said microfluidic cavity or said hydrophilic and/or porous material; - providing, by the battery , electrical energy while the fluid impregnates by capillarity the microfluidic cavity or said hydrophilic and/or porous material; and - connecting at least one instrument to the battery , wherein said instrument is designed such that its equivalent impedance makes the battery work at a specific operating point that allows determining the electrolytic conductivity of the fluid via a Direct Current, DC, mode method, and wherein the instrument quantifies said electrolytic conductivity of the fluid from the electrical energy supplied by the battery , such that the electrolytic conductivity of the fluid is inferred from the performance of the battery . - providing a battery comprising an oxidizing electrode and a reducing electrode separated at a distance and connected by a hydrophilic and/or a porous material or an empty receptacle providing a microfluidic cavity, wherein the battery is sensitive, only, to the presence of analytes with ionic charge that determine an electrolytic conductivity of a fluid to be sensed, the fluid acting as battery electrolyte and not as a fuel, wherein the oxidizing and reducing electrodes are connected through the fluid , wherein an internal resistance of the battery depends on said electrolytic conductivity of the fluid , and wherein the battery is activated upon the addition of said fluid to said microfluidic cavity or said hydrophilic and/or porous material; wherein the battery is sensitive, only, to the presence of analytes with ionic charge that determine an electrolytic conductivity of a fluid to be sensed, the fluid acting as battery electrolyte and not as a fuel, wherein the oxidizing and reducing electrodes are connected through the fluid , wherein an internal resistance of the battery depends on said electrolytic conductivity of the fluid , and wherein the battery is activated upon the addition of said fluid to said microfluidic cavity or said hydrophilic and/or porous material; - providing, by the battery , electrical energy while the fluid impregnates by capillarity the microfluidic cavity or said hydrophilic and/or porous material; and - connecting at least one instrument to the battery , wherein said instrument is designed such that its equivalent impedance makes the battery work at a specific operating point that allows determining the electrolytic conductivity of the fluid via a Direct Current, DC, mode method, and wherein the instrument quantifies said electrolytic conductivity of the fluid from the electrical energy supplied by the battery , such that the electrolytic conductivity of the fluid is inferred from the performance of the battery . <EOS>