A system (10) for establishing bypass of a failed battery cell (18) includes a failed cell sensor (26) which on sensing a failed cell generates an electric signal that destroys clamping relation of two retaining wire spools (24) to release retaining means (14,16). Such release enables a unitary plunger assembly (28) to be moved by a spring (49) to position a cylindrical pin contact (52) in electrical shorting relation to the first and second electrodes (57,58) connected across the cell (18).