Ash doesn't know about Motor Drive

After seeing two episodes of the anime, where Ash battles Electivire (one used by Volkner in the Sunyshore Gym and the other by Paul during the Sinnoh League) he seems to forget about Motor Drive. He has had Pikachu battle Electivire and ends up using an Electric-type attack which Electivire is IMMUNE to due to that ability called Motor Drive.