In Short, NO. Some folks never put a dime of U$D into their accounts, but I have. HOWEVER, That being said, you do get "voting power" (VP) that you "use up" every time you vote. if you are on maybe a 20 hour away schedule, you will replenish 16% of your Used VP. So in that sense it is FREE. Mine is low because I like to 'spread the love' around a Lot!
I will fetch you a link that will have a lot of helpful analytics for you to check! BRB