When Madara was fighting Gai, he had a lot of chakra: his own), Bijuu, Juubi, Mokuton, the elemental chakra, and Indra's reincarnated chakra (that might be considered part of his basic chakra). I don't understand why Madara would tell Gai that Gai almost killed him when Madara had all chakra that would let him heal and was almost as strong as Hagoromo (even Hagoromo said this when talking to Naruto).
From the Yin-Yang Release article on Naruto Wiki:
From the Yin-Yang Release article on Naruto Wiki:
Were Hagoromo to give his chakra to Gai, how would it be different if Gai had Yang chakra to fight Madara than if he used Yin chakra to fight Madara?Yin relates to one's spiritual energy and Yang relates to one's physical energy, and it's necessary to utilise both of these in order to mould chakra for ninjutsu.