Steem power is your influence and it replenishes over time remember you dont want to upvote more than like 10 times in a 24 hour period because it will drain your influence strength. Strength not steem power. Example: you start with 100% strength and then you upvote someone your strength drops to 98% then you vote again you drop to 96.5% then vote again you drop to 93%.
Check out this link it will tell you where your precentage is at as of current.
https://steemd.com/@franciferrer