APPLE INSIDER
Apple is investigating how to make the battery in an Apple Watch move in order to provide haptic feedback to the wearer.
Future Apple Watches may use a battery that moves to provide haptic feedbackApple is continuing its efforts to make Apple Watch thinner, this time by looking to remove the need for a standalone Taptic engine. Instead of space being taken up by that engine, Apple is looking to see if it can instead make the battery do double duty as a haptic feedback source.
Source: APPLE INSIDER