There isn't much to regenerating Pikachu's electricity. Actually, it's fully regenerated at the start of every day. When Pikachu uses its attacks, Thunder Shock, Thunder Bolt, or Thunder, it consumes its electric energy. When its energy is fully gone, it can't use electric attacks. To regenerate electricity, don't let it use its electricity for a while and it should slowly recover. To regenerate faster, feed it something good, like cupcakes, strawberries, raspberries, sunflowers, and I can go further. That's all you need to do to get back some electricity. =3