Perhaps Apple is indeed going to use "solid state batteries" in the iWatch. According to a
german news article (sorry - not allowed to access Google translate here) so far those have been used in highly specialized sensor applications and similar areas, where high cost and low production volume is less of a problem.
Technologically the liquid electrolyte is replaced by a solid material. This is said to give significant increases in battery time as well as space savings and improved safety.
Company "Applied Materials" has now announced to introduce a new production method to solve problems in material processing and make solid state batteries affordable. The company claims that the new method allows for producing prototypes close to mass production status and that the necessary new machines are already in use by customers in the battery industry.
One of the first uses will be in the "Wearable" sector, according to the company.