While the robots' efforts are important, they don’t run on courage alone. If their energy is depleted, they will be beamed back into the Astrotrain. After taking too much damage, a bot will have to recharge its armor.

Should you attempt to enter a level with an uncharged character, you will be asked to recharge it first. Simply tap the heart to start recharging. If a character is upgraded or if you scan its Telepod, its armor will be automatically recharged!