I have changed both the tensioner and the idler pulley and have installed a new battery. Yet the squeal is still there if the car runs for about 30 minutes or so the noise fades and is no longer there after an hour of run time. But after a cold start it is noisy as h*ll.
Make sure there isn't a glaze building on the belt from dirty pullys. Also, make sure there isn't coolant or oil getting on the belt. Since you replaced the tensioniers, they SHOULD be fine. If they are and nothing is getting on the belt, chances are one of the belt driven components is locking or going bad.