Skill
Energy (Duck Life 2)
Energy keeps the duck going during races and is raised by feeding.
Feeding
Buy food from the home-screen dispensers. 
Seed gives 0.6 energy levels and 
Super Seed gives 3. Both original Flash and later editions use these amounts.
Racing
Energy is separate from the four speed skills. The duck can run out of energy during a race and lose even if it has trained well. Feed it before longer races and raise the 
Maximum Level Upgrade when the cap prevents more progress.
Visible levels
The later-edition home display rounds levels down. A normal seed can therefore raise energy without immediately changing the visible whole-number level.
Across the games
Compare games and editions on the 
Energy page.