I think the auto battle feature should be available if you have enough healing potions in your inventory, the game should check your current health and your current armor and the calculate the amount of damage you will take, and if it reaches negative it should use some of your healing potions, but if you don't have enough potions, it shouldn't let you, also it the calculation should be based on an idiot, so the players would be rewarded for playing the battle themselves.
I know it will take a lot of work but the game would become very brain dead if playing the battle yourself wouldn't be rewarding enough after you earned the auto battle.
And as for when it should become unlocked, I think after you upgrade your armor to a level to unlock it, because currently armors are useless, the amount of money that you spend on them can be spent on way more healing potions that can be even more useful to you. Making the auto battle require max leveled armor should be a good way for both making the armors more useful and making sure the battles are so easy for the player when they reach this point in the game.

Tittle: Should we add an auto battle 

Maybe if you add it in such away that makes it a natural part of the game. For example

1) The witch functions as a merchant why not it make so that she also works as an enchantress/researxher for the character. 

You would bring her a certain amount of a particular drop from a enemy and after x amount of days you visit her again hence you gain some knowledge that allows the character to easily defeat the enemy (unlocks auto battle feature for that particular enemy).

Auto-Battle should also come with drawbacks such as reduced health after successive battles and reduced loot

after beating a monster X ammount of times there should be an option to spend whatever resources it would take to do the battle and get the rewards but without actually have to play through it

Yes to auto battle. After beating enemies a certain number of times sounds like a good metric for it.

Maybe after having defeated an enemy a certain amount of times or through an object you can equip (which you should get in the mid point or later on in the game).

I agree with some of the comments below where you have to beat an enemy a certain amount of times to auto-battle that specific enemy.

I like the ideas of a quest thatbwould unlock this feature. Personallyi like the rpg elements of a battle - but it can be a little boring when the mechanics are over-simplified.

Perhaps less rewards and unlock after mastering the Hunt arear after x many compleations of the same battle 

Maybe a "Beat fight X times to unlock auto battle", and make X higher depending on depending on the rewards

Yes. Combat is very repetitive at the moment. And there isn't many new cards to be excited about.

yes

If the intention is for farming materials to be an activity that the final game promotes rather than allows, then yes.

One threshold could be defeating that type of enemy without taking damage. You could cheese it and play the combat real slow but if you're willing to do that you're probably willing to grind materials. 

This would likely break down at enemies that deal poison or bleed damage as that seems unavoidable. One work around could be end the combat with full health without having used a healing item (health cards allowed). 

One thing to note, it seems like hunting in the enchanted forest uses a time bar, but hunting in the cave does not. Not sure if that is intentional.

Yes

EDIT: Alright personally I prefer watching the fights rather than skipping them, I would like the Auto to take over the combat when farming materials. It would be nice if we can enable and disable it at any point of the combat.

Auto-resolve the battle would also be appreciated, but am unsure what the conditions for enabling that should be.  Maybe you could add hidden "power score" for the MC and the monsters? and if the difference is significant enough, allow the use of Auto-battle?