Which potions do you like?

Potions are essentially like spells, so you need to spend a turn on them, and only on mage and healing potions. The rest should be consumed before the battle.

You can drink mage and healing potions (if the commander is injured) before the battle. You can drink mage potions until you're full; even if you have 100 and the accumulated mana, it won't disappear, and even if the hero flees during the battle.