Lol, invaded konoha, Destroyed konoha, fought naruto sage mode with 2 times sage chakra refil, fought 6 tails, used chibaku tensei, fought naruto sage mode again... ofc he was low on chakra.. and u saw before he died with res tech... he grew white hair and got old, so i think, then less chakra he has, the more he ages and gets in verge of death
He couldn't move without wheelchair thingie cuz at young age hanzou's jutsu burned hes legs to crisp.. he was depressed and didnt have any faith on himself anymore, + moment he summoned GM statue like ten rods pierced hes back and used nagatos chakra and rockn roll. + felt like he didn't rest at all or he was sick or something.. coughing blood etc.
Also, he was controlling 6 pains, and the attack he used to destroy Konoha takes alot of power as well, and it was the first time the attack was showed, but I think he also used it before...