s7 Edge sceen goes very dim at 30% battery life remaining

When my S7 Edge has 30% battery life remaining, the screen goes so dim that it is very difficult to see the screen to the point I can use the drop down to brighten up the display.

Also, the system seems to slow down dramitically.

I have already turned off all power saving features and it makes no difference.

the phone has been dropped and the screen is cracked. Not sure if that has anything to do with the screen going very dark at 30%.

thanks