There currently is one option to travel by night train from Padborg (Denmark) to Linköping (Sweden), taking approximately 7 hours: Namely the EN 344 operated by RDC.
RDC Euronight is a night train operated by RDC Deutschland connecting Berlin with Stockholm via Hamburg and Copenhagen, running three times a week in each direction.
The train offers two sleeping car categories. In the 1st class sleeper, private compartments accommodate up to three people with wide, made-up beds, a private bathroom with shower and toilet, and breakfast served directly to the compartment. The 2nd class sleeper has two-person compartments with a washbasin and 230V socket in the compartment; the toilet is in the corridor. 2nd class sleeper compartments can be booked privately or shared — in mixed or women-only configuration.
Couchette compartments accommodate up to six people and can be booked privately or as individual berths. All berths come with a pillow, sheet, and blanket. Washrooms and toilets are available in the carriage.
The seating car is the most affordable option, offering compartments for up to six people as well as open-plan carriages. Power sockets are available at every seat and a seat reservation is included in the ticket price. Toilets are located in the vestibules at the end of the car.
Passengers in sleeping car compartments — both 1st and 2nd class — receive breakfast delivered to their compartment. Couchette and seating car passengers are not provided with breakfast.