How can Miles be "Hundredlives" with his Feruchemically and Allomantically power?

I'm a reader from HK and i've finished Mistborn Trilogy a month ago,i'm now reading Mistborn : The Alloy of Law , and i got a question. ^{I don't know if it's a chinese translation problem} How can Miles achieve immortality with his twin born power, gold used to store helth(right?) but how do Allomantically help the Immortal equation? he can save his helth in gold ,then... Burn it(?) isn't it the same with Tapping it?Pls tell me how do he be "Hundredlives"

(BTW, this is my first time using social media to talk about mistborn,is this the biggest group to discuss or is there other bigger media to talk