The Apple Watch may be an elegant device, but it does not have a long battery life. Many accessory manufacturers are already working on cases, stands, and screen guards for the Apple Watch. But will we see a decent Apple Watch battery extender this year? The Reverse Strap happens to be just that. It extends the battery life of the Apple Watch by up to 125%.
The Reverse Strap has a 400 mAh battery and a magnetic inductive charging cradle to power your smartwatch. You will probably have to wait a while to get your hands on one but you can already pre-order a Reserve Strap to show your interest.[Source]