A vent system for exhausting gas generated within a battery case is provided. The vent system exhausts gas from the battery case (12) while maintaining the hermetic seal of the case. The vent system provides a small gas exit hole (16) that is sufficiently small to prevent electrolyte leakage and also intake of excess carbon dioxide or excess water vapor from the atmosphere. Also, various combinations of gas-permeable, hydrophobic membranes (40, 44) and diffuser material (42) may cover the gas exit hole to provide humidity control for the battery while exhausting gases from the battery. A recess (36) may be provided within the case such that the gas exit hole communicates between the atmosphere and the recess. Also, various combinations of gas-permeable, hydrophobic membranes (40, 44) and diffuser (42) material may cover the recess and gas exit hole to provide humidity control for the battery while exhausting gases from the battery case. The present invention also provides a vent system in which gas-permeable, hydrophobic membranes and diffuser material may fill an opening so as to exhaust gas from the case. The present invention also provides an electrode lead (39) which extends along the battery case and through the seam (34) of the battery case in a manner in which a hermetic seal is provided around the lead. The manufacturing process for the seal around the lead is relatively simple.