Non-woven fabric base material, and battery separator

The objective of the present invention is to provide a non-woven fabric base material and a battery separator with which it is possible to prevent the occurrence of internal short circuits, without causing a deterioration in discharge capacity under large currents or low temperatures. In a non-woven fabric base material 11 used in a battery separator 10, if an initial thickness measured using a micrometer is T0 ([mu]m), a minimum theoretical thickness obtained using the following formula A is Tmin ([mu]m), and a difference between an amount of displacement Dmax ([mu]m) under maximum loading and an amount of displacement Dmin ([mu]m) under minimum loading, when a loading-unloading test is performed using a plane indenter having a diameter of 200 [mu]m under the following conditions, namely a maximum load of 1.96 x 10-3 N, a minimum load of 0.0196 x 10-3 N, a holding time of 2 seconds, and a loading speed of 0.142 x 10-3 N/second, is a recovery amount R ([mu]m), a compression change ratio calculated using the f