Display flicking problem

I have a strange problem with my Powerbook 12'' G4. When the energy reaches 2%, the screen starts to flick(the brightness slighty increases or decreases rapidly). When i plug the AC adapter, the problem disappears. This is odd, since i haven't noticed anything for the first month after buying it.I have asked another person if they saw something strange in the display, and that person replyed that the screen looked fine.
I don't know if this normal or not, but i think this must be related to a energy problem.