The present invention concerns a device for mounting a source of electric energy (100), preferably a button-type battery, for a portable electronic apparatus including a housing (3, 44), closed by a cover (14, 49), for said energy source. The housing includes, in proximity to its periphery, tongues (5, 32) that can be deformed for holding the energy source axially in the housing. Further, the cover includes a wall (15, 50) projecting into the housing and arranged between the periphery of the housing and the tongues retaining the energy source. The wall of the cover thus ensures that the tongues are held properly against the energy source when the latter is arranged in the housing, in particular in the event of a violent shock.