Pokemon Best Wishes! - episode 62 - 11 Jan, 2012

After earning the Quake Badge, Ash and co. decide to head to Mistralton City next. Along the way, however, Ash notices Pikachu has fallen ill, and soon learns that a Joltik was feeding off Pikachu's electricity, as well as Iris' Emolga and Cilan's Stunfisk (being part electric). They eventually find out that Team Rocket is behind this phenomenon. (Source: Wikipedia)