It will last 1 min. It will recharge player life with 1% of damage taken. If you will want to use it again you will need to wait 5 or 10 min. I hope you will add this skill.
For example: You have a book of magic but you need books of range. So you can change this book of magic for one book of range. And maybe you will need to pay 1k to change it. Book of skills can not be changed.