Goodnotes battery usage on iPad Pro

I bought an iPad Pro 11 inches about one year ago. and I use mostly Goodnotes, which is a magic keyboard and pen attached to the iPad. and it gives me charged about 4-5 hours. I want to know other users experience about their iPad battery life. who use Goodnotes a lot. in this condition, I'm wondering if 4 hours is the acceptable battery.

I don't watch a movie or play games on my iPad at all. I just read a PDF on Books and Goodnotes.