The Energy cost for playing battles depends on:

➡️  Your Magician Level

Your current Magician Level is displayed on the top left corner of your screen.

As your Magician Level advances and you progress through Quests, the Energy cost increases as well.

➡️  Battle difficulty

The number of Stars shown on the map represents the battle difficulty.
 
1⭐ battles -  Easiest
2⭐⭐ battles - Moderate difficulty
3⭐⭐⭐  battles - Toughest (but you get more rewards upon winning)

In case 3-Star battles are too challenging, try your hand at 2-Star battles! You have a greater chance at victory and will still earn Magic Cards to upgrade your spells! 

💡Learn more about: How much Energy does a battle cost?