Indeed, it is difficult. I suppose best strategy is to prioritize reaching Fountains of Health as quickly as possible, while using Thrall (and his abilities) to scout ahead and cover your low HP units. Furthermore, focus on Centaur Archer since they are hitting hard.
This is the chapter I hate the most
I try to regain HP from my troop from resting
But the foes keep coming and I nearly lose all my troop
Indeed, it is difficult. I suppose best strategy is to prioritize reaching Fountains of Health as quickly as possible, while using Thrall (and his abilities) to scout ahead and cover your low HP units. Furthermore, focus on Centaur Archer since they are hitting hard.