I am able to adjust the percent of the brightness with the keys and slider, however, the brightness change only applies once I plug my computer into the charger. I have updated the graphics and display drivers multiple times and nothing seems to work. Please help, thanks!
Then, contact HP for support of their device. They are the integrator, they made the device, and they supposedly tested the drivers they provide. Additionally, these drivers have likely been modified by HP. You may also want to update the HP bios to the latest they have available.
When you purchased this device, you paid HP for support. Make them earn it.