If you can do get another battery to test with.
Many laptop backlights don't work off the battery directly but will increase the voltage (sometimes actually quite a bit higher). This is one of the things that can die and make screens stop working. Signs of impending failure of that can be this sort of flickering.
Other options include if you are moving the screen to take the power out (common for one of those back powered ones) then the moving it can tweak the ribbon and cause this, or said power lead adds that little bit of stress to the motherboard (in most laptops with back power or side power at the back it is but a few mm from the screen ribbons) to have the connection come good. If you turn it off, or pull it if your sockets don't have switches, at the wall that can also help diagnose this one.
If power decreasing modes (on the flip side what happens if you stress the CPU in this mode) lessen it then it is more likely to be the battery struggles to put out enough current or voltage for the inverter section.