I waited 10 minutes for it to charge, but it still says the master sword is low on energy. When I tried to defeat one of the divine beasts it broke.
1Just as an aside, The Trial of the Sword, introduced in the first DLC in June 2017, will remove the requirement for the Master Sword to recharge. Upon completion of all 3 sections of the trial, the sword will remain at its full power permanently, and never break.– CodyJul 5, 2017 at 22:33
Like the champion powers, the Master Sword does not begin regenerating until it is completely used up. Keeping it in your pocket when it's weak does not help you get it back to full durability faster - you have to expend it to zero before the timer starts.
3Any time my Master Sword is starting to get low, if I'm not in the middle of a battle, I will just purposefully break it by slamming it on the ground so that it can start the recharge. It's one of my very few complaints about the game; I wish it would just recharge any time it wasn't equipped. Jun 19, 2017 at 16:23