Apple’s official entry into the wireless charging market is a major blow for Energous.

After Apple provided details on Tuesday about the wireless charging capability in the latest iPhones, shares of Energous, the maker of WattUP wire-free charging, plunged as much as 21 percent.

Apple said it’s using the Qi wireless charging standard, the technology that’s also used for wireless charging in mobile devices from Samsung and other device makers. The company will start selling a wireless mat next year.

The iPhone 8 and iPhone 8 Plus, which were also introduced on Tuesday, go on sale on Sep. 22. The iPhone X ships on Nov. 3.

An Energous executive in 2015 said that it was working with “one of the top five consumer electronics companies.” That company is clearly not Apple.

Energous shares are highly volatile, frequently rising or falling by 5 percent or more in a day. The stock was briefly halted after Apple’s announcement and then bounced around. It was down about 11 percent when the event ended.

The company is valued at $243 million.