The battery run time is 9hour is it in full brightness mode or medium or low brightness mode

Apple’s quotes the runtime as “up to” nine hours. Hight screen brightness and/or CPU/GPU intensive Apps will consume more power - and reduce the available runtime before the iPad must be recharged.

You should perhaps assume that quoted figures might be achieved in ideal conditions. While not to my knowledge explicitly defined, 30-50% screen brightness might be anticipated in normal ambient room lighting. Increasing the screen brightness to 100%, you should expect considerably shorter battery autonomy.