For years, companies such as Samsung, Nokia, LG and others have sold smartphones with wireless chargers, meaning the devices can power up by simply being laid down on charging pads using components that are built into the devices.

Wireless charging, though, has failed to take off because of one major holdout: Apple, which has never outfitted its products with the parts necessary for wireless charging. But that could soon change.

The U.S. Patent & Trademark Office on Thursday published an application filed in early 2013 by Apple for a patent on wireless charging technology that shows how it could be used on a smartwatch or other Apple products.

Analysts offered reasons why Apple has never used wireless charging for the iPhone but may want to use it on a wearable device.

Van Baker at Gartner Relevant Products/Services said Apple has kept wireless charging off the iPhone because it would require more internal components, which would lead to a thicker design and higher manufacturing costs.

"It's for a feature that a lot of people don't necessarily value when it comes to smartphones," he said. "So why increase materials when you can't get value back for it? That's a trade-off they weren't willing to make."

But smartwatches use smaller batteries than smartphones, so adding wireless charging components inside the gadget wouldn't increase size as drastically as it might on a phone, Baker said. Additionally, wireless charging allows for more elegant design than a charging cable port would, Baker said.

Besides style points, wireless charging also improves a smartwatch's resistance to moisture, water, dirt and dust, which isn't as important for smartphones because they can be put in cases and are often kept in pockets, said Christian DeFeo, an expert in wireless charging and the innovation manager for Newark element14, a high-service distributor of technology products.

"Watches are fixed to our wrists. They don't come in cases. They're supposed to be knocked around as we make our way through the world," DeFeo said. "Adding wireless power to a watch like that helps to answer some of the resilience questions."

Reports have also said Apple's smartwatch will be focused on health and fitness tracking, so it's important that users wear the device at all times. That could be possible if users can power up by laying their wrists on charging pads while they work at their desks, said J.P. Gownder, an analyst at Forrester Research.

"If it's a health tracking technology, you really don't want to take it off -- you want to wear it all the time," Gownder said.

Apple's patent application says the wireless charging technology could also double as an antenna for near-field communication, a technology that allows a device to easily talk to other NFC-enabled gadgets. Gownder said an Apple smartwatch could use NFC technology to make wireless payments, unlock doors with NFC chips or even start a car that is NFC-enabled.

"A smartwatch should help you with real-world scenarios, things that you need immediately -- not pull out your phone and type your pass code," Gownder said.

We might not have to wait long to find out how, if at all, Apple uses wireless charging. The company on Thursday announced it would hold an event Sept. 9, where some reports have said it will unveil its first wearable device.