The Endorfy Thock 75% (DE, Wireless) keyboard is indeed a wireless option, but specific information on battery life or operating time in wireless mode is not explicitly mentioned in the sources provided.
However, it can be assumed that the keyboard, like many other wireless keyboards, has a battery-based power supply. For exact information on battery life or operating time in wireless mode, it would be advisable to consult the user manual or the manufacturer's official product page, as these details may be given there.
It's the same for me. I then simply unplugged the keyboard. Once it stopped lighting up, I assumed that it was fully charged, which it probably was. But it takes a very long time...