(JP2000294217-A)   NOVELTY - The battery separator comprises: (i) a sulfonated fiber obtained by sulfonating a polyolefin resin fiber having an intrinsic viscosity number of 0.2-1.0 dl/g; (ii) a polyolefin resin fiber having sulfonic groups introduced uniformly on surface of the fiber; or (iii) a fiber obtained by sulfonating an oxidized polyolefin resin fiber. The separator has an ammonia-trapping rate of at least 80%.    USE - As a battery separator.    ADVANTAGE - The battery separator has an improved ammonia trapping property of at least 80% without a significant strength deterioration of constitutive fibers of the separator. Using the separator provides a battery that exhibits a less self-discharge and a satisfactory capacity-holding rate.    (JP2000294218-A)   NOVELTY - The battery separator comprises: (i) a sulfonated fiber obtained by sulfonating a polyolefin resin fiber having an intrinsic viscosity number of 0.2-1.0 dl/g; (ii) a polyolefin resin fiber having sulfonic groups introduced uniformly on surface of the fiber; or (iii) a fiber obtained by sulfonating an oxidized polyolefin resin fiber. The separator has an ammonia-trapping rate of at least 80%.    USE - As a battery separator.    ADVANTAGE - The battery separator has an improved ammonia trapping property of at least 80% without a significant strength deterioration of constitutive fibers of the separator. Using the separator provides a battery that exhibits a less self-discharge and a satisfactory capacity-holding rate.    (JP2001135297-A)   NOVELTY - The battery separator comprises: (i) a sulfonated fiber obtained by sulfonating a polyolefin resin fiber having an intrinsic viscosity number of 0.2-1.0 dl/g; (ii) a polyolefin resin fiber having sulfonic groups introduced uniformly on surface of the fiber; or (iii) a fiber obtained by sulfonating an oxidized polyolefin resin fiber. The separator has an ammonia-trapping rate of at least 80%.    USE - As a battery separator.    ADVANTAGE - The battery separator has an improved ammonia trapping property of at least 80% without a significant strength deterioration of constitutive fibers of the separator. Using the separator provides a battery that exhibits a less self-discharge and a satisfactory capacity-holding rate.