"I want to top up 100 Yuan."
The English here currently ("I want to top up 100 Yuan") is wrong. The money being put on the card isn't what's topped up (though it is the top-up, or the amount of the top-up). What's topped up is the card, or the amount of money on the card.
More literally, then, this sentence means "I want to recharge with one hundred units", where the "units" are not necessarily yuan, but could be US dollars, among other things, and therefore "dollars" should also be acceptable. Some possibilities, in five parts:
 I want to / I would like to  top (it / my card) up / recharge (it / my card)  with/by  one hundred / another hundred  yuan/dollars.
The bits in round brackets are optional. A slash denotes a choice.
Other options would be along the lines of "I want to put another hundred yuan/dollars on (it / my card)".
Also, "yuan" shouldn't be capitalized, any more than "dollars" or "rupees" would be.
You're not wrong but you're not right. I would probably say, "I want to charge 100 yuan to my phone" but in Chinese you don't really need to say "to my phone" since you don't commonly charge money to anything else.
Thank you for the clarification. I am a native American English speaker and I've never heard of "topping up" before. Appatently, it's British. We do say "top off" for things like drinks and the gas in car, but we don't use it for money.
Isnt kuai //kind of// colloquial for yuan? I may be wrong, just had this thought in the back of my head
Only in some places, they more frequently say yuan in most of the country, and if you do say 快 you should say 块钱 to indicate you're talking about money