Rakan 2nd E Cannot Cast at Low Mana

If Rakan brings himself under sufficient mana to cast his E, Battle Dance, he is unable to recast the ability despite it being free. That is to say if he casts Battle Dance and brings himself under 60/70/80/90/100 mana, or if he casts Battle Dance and any other of his spells that result in him having less than that much mana, he cannot recast Battle Dance for free.