A secondary cell featuring a transient rise in temperature once charged to saturation is coupled and thereby forms a composite structure with a charging assembly by mutual engagement of conductive contacts provided on either part. The force of union generated by the coupling compresses a thermosetting prestressed means which is a spring or other prestressed element the coupling brings the contacts into conduction to initiate charging. The stress is released once charging in the secondary cell reaches its saturation, followed by cutoff of the charging current to the secondary cell.