The thousands of Apple Watch owners who purchased a pricey Reserve Strap to give their wearable some extra juice are basically up the creek without a paddle. Because those $249.99 battery bands no longer work as intended.

Reserve Strap on Monday revealed that Apple's recent WatchOS release "remove all functionality from Apple Watch's accessory port thereby blocking Reserve Strap's ability to charge" the high-tech watch.

"This was a deviation from how the port functioned in all previous WatchOS releases and appears to have been a deliberate effort to block development of third-party smartbands," the company wrote in a note on its website. "This action was surprising given that prior to this WatchOS update, Apple had been an advocate of our product–going as far as inviting us to Cupertino to show them early prototypes as well as placing pre-orders for many Reserve Straps."

Apple did not immediately respond to a request for comment. Reserve Strap is now calling for Apple to "remove the intentional blocking" and once again allow customers to use their to battery bands as intended.

The band still works on Apple Watches running WatchOS 2.0 or earlier, but those who want to keep using the strap for extra juice "will not be able to update their Watches without losing the charging feature that is only present in the early versions of WatchOS," Reserve Strap warned.

At this point, the company is no longer taking new orders on its website, but said it will continue shipping straps over the coming weeks to customers running the older software. Reserve Strap asked customers to contact Apple about the matter.

"For other customers, we are continuing to explore additional charging protocol solutions and believe an official MFi program supporting Apple Watch smartband accessories may be forthcoming," the company wrote.