A diode for alternating current electrostatic discharge protection circuit is formed in a silicon germanium hetrojunction bipolar transistor process that utilizes a very thin collector region. The two or more magnetic elements contain a magnetic element having fewer than 5 effective d electrons and a magnetic element having more than 5 effective d electrons, and a total number of effective d electrons of the two or more magnetic elements is 10 or a value close to 10. The inner surface of the receiving hole has a sunken slot with an inner circular arc surface. A first set of voltage drops between a positive electrode and a negative electrode of each battery cell in the battery pack is also detected. 1, the sheet additionally being such that the flexural stress at break in a \u201cring-on-tripod\u201d test is at least 70 MPa, after Vickers indentation under a load of 60 N.