Screen Brightness Dims when battery is below 50%. any reason why ? how to fix it ?

Hi.

so I noticed something with my Oneplus Two. I am not sure if its because of the kernels or its like that form the start.

my wife has HTC ONE M9+, when my battery is full or above 50%, my screen is brighter than her screen. we use the google page from the browser to compare colors. however, when my battery is lower than 50% ( I tested it today when it was around 40% or 38% battery remaining)

and her screen was brighter than mine.

I tried all three kernels available. and all the same results. and the auto brightness is already unchecked.

any idea why this is happening ? the problem is I don't have the official kernel and I don't want to format my phone or whatever to get the stock kernel to test this again.

the only reason I actually went ahead and installed a custom kernel is because in my eyes the colors of the phone was a lil washed out " true to life but not to my liking" as I am used to more color options.

any reason why this is happening and is there a way to fix this ?

thanks in advance to anyone who can actually help.