A method for encapsulating a thin-film lithium-ion type battery, including the steps of: forming, on a substrate, an active stack having as a lower layer a cathode collector layer extending over a surface area larger than the surface area of the other layers; forming, over the structure, a passivation layer including through openings at locations intended to receive anode collector and cathode collector contacts; forming first and second separate portions of an under-bump metallization, the first portions being located on the walls and the bottom of the openings, the second portions covering the passivation layer; and forming an encapsulation layer over the entire structure.