I returned my car at 4.45am this morning at Lisbon Airport. I fully refuelled the car last night and tried to stop at petrol stations near the airport to top up again. However, they were not open at that time and my display had just dropped to 7/8 full. I fully accept that I should be charged the cost to top up (even at an inflated rate). However, I have been charged 50 euro additional penalty, which is completely unreasonable. At no point was this fee explained to me. You may have it buried in your terms and conditions but this is totally unacceptable and I would like to complain formally. User's recommendation: If you are returning early in the morning, you risk not being able to fill your car.