I understand that on certain motorways in Portugal, probably extending to include all motorways, if you have an foreign registered vehicle, the only way of paying the toll is by obtaining a DEM at a cost of 27 euros (redeemable on return) and by preloading it with a minimum of 10 euros. What happens when this amount runs out. Are further tolls charged to a linked credit card or is it necessary to anticipate the costs and preload this amount, or do you get charged the extra on return of the DEM? Is there another possibility I have overlooked? I will be driving a private French registered vehicle, traveling around 1500km on motorways over 6 days.