The only way to keep it at full power is not upvote and don't post.
Upvoting (and by having that box checked, you upvote your own posts) takes $ out of your vote power, each upvote does.
Now, I'm told that you are allowed between (depending on who you are talking to) 4 and 11 full, 100% upvotes per day without it affecting your vote power.
If your V power is down, and you stop upvoting, it gradually comes back up (I think each time someone upvotes you).
I for sure don't understand it all clearly, yet, but these are the way I understand how it works.