I bring my Illinois IPass (EZPass compatible) when I travel east. I make sure the little box is closed and hold my transponder up to the windshield when passing thru a toll. To be extra sure its reading, when you can, you could got thru "manual" lanes if they exist and wait for the read before proceeding thru. The only problem I've ever had is forgetting my pass in the rental when I used to stick it to the window. Now I leave it in door handle and take it out as needed. Haven't forgotten it since (knock on wood).

Some toll authorities do allow adding rental cars temporarily to the account (Illinois does), but I haven't done that in a while.