If you have power issues or want to hang lights in places where you don't have a power outlet, battery operated lights are the best lights for you. They run on batteries/cells that you can easily replace every time they run out. This way, you will be worry-free about your lights going out if the power goes off.
They can be hung in places where you don't have a power outlet like your balcony, wreaths, your garland, curtains, etc. They make your indoors and outdoors look cosier and warmer, especially to guests during the cold Christmas season.