Pichu evolves by happiness.
pichu does not evolve at a level,it evolves with a high friendship.Pichu can evolve at any level if it has enough friendship.
pichu evolves by friendship so when it likes you enough it will evolve no it dosent it evolves at level 20
sentret evolves at level 20 in Pokemon heartgold
Ampharos does not evolve in Pokémon HeartGold.
AnswerI'm not quite sure what Pokemon Battle Arena is (Pokemon Battle Revolution?), but Pichu does not evolve at a certain level. Like the majority of the Baby Pokemon, Pichu evolves once it's happiness is high enough and then Leveled up.
It evolves with friendship
it evolves at lv.59
It needs enough friendship with you.
when it has high friendship
Level 36
Level 15.
level 30