An automobile battery, which is a lead-acid battery, comprising: a plurality of anode plates, for storing electricity in a chemically reactive state, formed in a mesh shape by forming a plurality of cuts in series on a lead plate strip rolled to a uniform thickness and performing expansion processing; a plurality of cathode plates, for storing electricity in a chemically reactive state, having a size identical to the anode plates and being in a mesh shape; a plurality of separators disposed between the anode plates and the cathode plates so that the anode plates and the cathode plates are electrically insulated and mechanically separated, the plurality of separators having an absorbent glass mat impregnated with an electrolyte, such that a chemical reaction for storing electricity is facilitated and an inner pressure of a cell is maintained constant; an upper case and a lower case, made of polypropylene and including a plurality of separate unit cells, each of the unit cells including the anode plates, the cathode plates, the separators and the electrolyte; and a cap screw-coupled into a screw hole formed in each of the unit cells of the upper case so as to exhaust a gas generated during charge and discharge when pressure of the gas is at or over a predetermined level, wherein the cap comprises: an outer cap screw-coupled into the screw hole formed in each of the unit cells of the upper case, the outer cap comprising a fixed cavity having one closed end at a central portion thereof and an open end, an exhaust passage connected to the closed end of the fixed cavity so as to communicate with outside, and a fixed fin and a pressure protrusion, which protrude in a form of a cone at a center of the closed end of the fixed cavity; an inner cap, inserted into the open end of the fixed cavity of the outer cap and fastened by a fastening lock, the inner cap including a gas hole having both open ends at a center thereof; and a valve, provided between the outer cap and the inner cap, the valve comprising a hinge membrane fixed to one end of the inner cap by the fixed fin, a pressure part connected to the hinge membrane and being in contact with the pressure protrusion so as to support a predetermined pressure and to block one open end of the gas hole, and a blockage membrane connected to the hinge membrane and the pressure part and configured such that one end of the gas hole is blocked and the blocked end of the gas hole is opened when the pressure part is not supported by a pressure more than the predetermined level. a plurality of anode plates, for storing electricity in a chemically reactive state, formed in a mesh shape by forming a plurality of cuts in series on a lead plate strip rolled to a uniform thickness and performing expansion processing; a plurality of cathode plates, for storing electricity in a chemically reactive state, having a size identical to the anode plates and being in a mesh shape; a plurality of separators disposed between the anode plates and the cathode plates so that the anode plates and the cathode plates are electrically insulated and mechanically separated, the plurality of separators having an absorbent glass mat impregnated with an electrolyte, such that a chemical reaction for storing electricity is facilitated and an inner pressure of a cell is maintained constant; an upper case and a lower case, made of polypropylene and including a plurality of separate unit cells, each of the unit cells including the anode plates, the cathode plates, the separators and the electrolyte; and a cap screw-coupled into a screw hole formed in each of the unit cells of the upper case so as to exhaust a gas generated during charge and discharge when pressure of the gas is at or over a predetermined level, an outer cap screw-coupled into the screw hole formed in each of the unit cells of the upper case, the outer cap comprising a fixed cavity having one closed end at a central portion thereof and an open end, an exhaust passage connected to the closed end of the fixed cavity so as to communicate with outside, and a fixed fin and a pressure protrusion, which protrude in a form of a cone at a center of the closed end of the fixed cavity; an inner cap, inserted into the open end of the fixed cavity of the outer cap and fastened by a fastening lock, the inner cap including a gas hole having both open ends at a center thereof; and a valve, provided between the outer cap and the inner cap, the valve comprising a hinge membrane fixed to one end of the inner cap by the fixed fin, a pressure part connected to the hinge membrane and being in contact with the pressure protrusion so as to support a predetermined pressure and to block one open end of the gas hole, and a blockage membrane connected to the hinge membrane and the pressure part and configured such that one end of the gas hole is blocked and the blocked end of the gas hole is opened when the pressure part is not supported by a pressure more than the predetermined level.