A battery pack comprising: - a plurality of electrochemical batteries or accumulators (A1-An), each comprising: • a housing or a flexible packaging, • a first output terminal and a second output terminal of an opposite polarity to the first output terminal; at least one of the output terminals comprising: • an electrically conductive part, • a magnetic lock comprising a permanent magnet; - at least one ferromagnetic part secured to an electrical connecting bar, called busbar, forming a closure plate of a magnetic circuit with the magnetic lock of the output terminal; the battery pack being configured such that: i/ in normal operation of the accumulator, the magnetic attraction force of the permanent magnet of the output terminal on the closure plate of a first busbar, in the closed magnetic circuit configuration, ensures the mechanical and electrical connection between the output terminal and the first busbar, ii/ upon a failure of the accumulator provoking an overheating thereof, the permanent magnet of the output terminal heats up and at least to a temperature from which it loses its magnetic properties, to the point of mechanical disconnection between the output terminal and the first busbar, characterized in that the disconnection causes the accumulator to drop through gravity. - a plurality of electrochemical batteries or accumulators (A1-An), each comprising: • a housing or a flexible packaging, • a first output terminal and a second output terminal of an opposite polarity to the first output terminal; at least one of the output terminals comprising: • an electrically conductive part, • a magnetic lock comprising a permanent magnet; • a housing or a flexible packaging, • a first output terminal and a second output terminal of an opposite polarity to the first output terminal; • an electrically conductive part, • a magnetic lock comprising a permanent magnet; - at least one ferromagnetic part secured to an electrical connecting bar, called busbar, forming a closure plate of a magnetic circuit with the magnetic lock of the output terminal; the battery pack being configured such that: i/ in normal operation of the accumulator, the magnetic attraction force of the permanent magnet of the output terminal on the closure plate of a first busbar, in the closed magnetic circuit configuration, ensures the mechanical and electrical connection between the output terminal and the first busbar, ii/ upon a failure of the accumulator provoking an overheating thereof, the permanent magnet of the output terminal heats up and at least to a temperature from which it loses its magnetic properties, to the point of mechanical disconnection between the output terminal and the first busbar, characterized in that the disconnection causes the accumulator to drop through gravity. i/ in normal operation of the accumulator, the magnetic attraction force of the permanent magnet of the output terminal on the closure plate of a first busbar, in the closed magnetic circuit configuration, ensures the mechanical and electrical connection between the output terminal and the first busbar, ii/ upon a failure of the accumulator provoking an overheating thereof, the permanent magnet of the output terminal heats up and at least to a temperature from which it loses its magnetic properties, to the point of mechanical disconnection between the output terminal and the first busbar, characterized in that the disconnection causes the accumulator to drop through gravity.