http://lindelectronics.com/cgi-bin/s...detail_product

"Note - This adapter can not be used in the airline in-seat power systems and it is not provided with the special connection cable. The air in-seat power systems are limited to an output of only 75 Watts."

AFAIK the 1100 and 5100 cannot be used with in-seat power, because they MUST have 90W of power (the other Dell laptops drop down their processor speed and disable charging of the battery, allowing them to be used with 75W). So the only option you have is using it in the car, or buying more batteries.