It is not yet skilled at storing electricity. It may send out a jolt if amused or startled.
Despite its small size, it can zap even adult humans. However, if it does so, it also surprises itself.
It is unskilled at storing electric power. Any kind of shock causes it to discharge energy spontaneously.
PICHU charges itself with electricity more easily on days with thunderclouds or when the air is very dry. You can hear the crackling of static electricity coming off this POKéMON.
When PICHU plays with others, it may short out electricity with another PICHU, creating a shower of sparks. In that event, this POKéMON will begin crying, startled by the flash of sparks.
— Pokédex entries (via PokeAPI)