This means for sure either you have loose terminal or calc deposit on terminals. Remove both battery terimal and pour some hot hot water on both terminals and socket, clean it nicely and wait till it dries, apply little grease and refix it tightly.
If still you have flickering after above excersise, then that means your alternator is on the way of expiring and soon you will be stranded on road side. If that happen, dont panic and switch off all lights, ac, music etc and you will be able to drive home atleast. As if battery is good it holds enough charge to keep your car running for few hrs w/o any other electrical overheads.