Apple Watch early adopters need worry no more about being out of time. Reserve Strap, a startup that has invented a band with a backup battery inside, is promising to extend the watch's battery life by more than 30 hours.

The newly released strap's specifications also show that the strap will add 65g of weight to the device. The strap has a width of 25mm, thickness of 3-9mm, and comes in a selection of white, black and grey. While the watch itself charges through a magnetic charging cable on the back of the device, Reserve Strap is has a separate micro-USB charger.

Apple's own specifications say the watch can last up to 18 hours out of the box, extending to 72 hours in power reserve mode. Mashable's review described the battery life as "the best surprise of all," while Walt Mossberg said his watch sometimes lasts longer than Apple said it would. Reserve Strap says the product will extend battery life by 2.7 times, suggesting it will be aimed at travelers and others without access to a charger at night.

Reserve Strap was able to make its product work via a hidden 6-pin diagnostic port on the watch. Although the port is hidden, the company says the strap "fully complies with Apple's Band Design Guidelines for the Apple Watch and doesn't violate either AppleCare warranty or Apple Terms & Conditions." Reserve Strap will start shipping Nov. 3, with each one costing $249.99.