I would normally compost them so it can be used to benefit the garden.
Homemade potassium fertilizer using banana peels is very easy to make.
If the leaves of your plant turn a purplish hue, the plant needs potassium.

Watch the tutorial, by Natural Ways, to learn the 6 ways to recycle your banana peels.
All of these ideas are quite easy and the benefits are well worth making the effort to do them.