....considering the S4 isn't currently available for hands on experience. It is possible that they are compatible, but don't count on it. Cell phone manufacturers usually make each device with it's own, unique battery. Form factor will probably be close but no guarantees......
is it possible to use the Galaxy S4 battery in my Galaxy S3?
i don't like using other 3rd party batteries, and loosing the S3 Slick design.