TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Component: The battery separator comprises:(i) an ammonia trapping non-woven fabric mainly containing the sulfonated fiber; and(ii) a reinforcing non-woven fabric composed of a material different from that of and laminated on the ammonia trapping non-woven fabric.Preferred Property: The separator has a total sulfur content of at least 1 mg/g separator and comprises at least 20 mass% sulfonated fiber. The battery having the separator has a capacity-holding rate of at least 60%.Preferred Method: Producing the separator for a battery involves oxidizing the polyolefin resin fiber by corona discharge or ultraviolet ray irradiation.    TECHNOLOGY FOCUS - POLYMERS - Preferred Properties: The sulfonated polyolefin resin fiber has a specific surface area of at least 0.5 m2/g as determined by the Brunauer-Emmett-Teller (BET) method. The sulfonated polyolefin resin fiber of the ammonia trapping non-woven fabric has a total sulfur content of more than 10 mg/g - less than or equal to 50 mg/gof sulfonated fiber or greater than or equal to 150 mg/m2. The sulfonated polyolefin resin fiber of the reinforcing non-woven fabric has an intrinsic viscosity number of 1.0 dl/g or more and a total sulfur content of more than 0 mg/g - less than or equal to 7 mg/g of the fiber. The bulk density of fabric trapping fabric is at least 0.5 g/cm3 and that of reinforcing fabric is less than or equal to 0.4 g/cm3. The average fiber diameter of the trapping fabric is 1-10 microns and that of reinforcing fabric is at least 10 microns. The fibers of reinforcing fabric have a rectangular or elliptic cross-section. EXAMPLE - A polypropylene non-woven fabric having a weight of 55 g/m2, a thickness of 120 microns, and an average fiber diameter of 5 microns was subjected to an oxidation treatment with an alternating current corona discharge and immersed in a 98% concentrated sulfuric acid at 95 degrees C for 60 minutes for sulfonation. The obtained separator with an ion exchange capacity of 0.042 meg/g was integrated into a battery having an ammonia trapping rate of 100% and a capacity-holding rate of 83% at 45 degrees C for 72 hours. A separator prepared in the same manner but without the oxidation treatment with corona discharge had an ammonia trapping rate of 79% and a capacity-holding rate of 58% at the same conditions.