In the shop a single Power Point's price is 2 coins. Fox example, 10 Power Points will cost 20 coins, 20 Power Points 40 coins etc. The amount of Power Points you can buy varies with the Daily Offer. Each Power Point offer can only be bought once. Power Point offers change every 24 hours and after that they can be bought again.
Better Brawl Boxes tend to give more Power Points to each Brawler. Once enough Power Points to get a Brawler to level 9 are collected, no more Power Points will be found for that Brawler. When all of the player's unlocked Brawlers have the maximum amount of Power Points, Brawl Boxes will no longer contain Power Points, and more Coins will be awarded instead.