RE: Exporting used Fluence from UK?
The £5,000 goes to the manufacturer on registration of the car. The private consumer has nothing to do with it.
Fluence battery in the UK is the property of RCI UK. It is not permitted to use the battery outside the UK for more than 30 days.
Nissan Leafs (sold with their batteries) are plentiful, though, and even if Renault were to sell the batteries with the cars, would still probably come to more than you can get a Leaf for. You can buy a Gen 1 or a Gen 2 non-flex car and import it into DK, no problem.
Don't fancy a Leaf?
There is a chap who has posted here from Czech that has bought Fluences from France though, battery-and-all. You might still find it is possible from French sources, buying the battery outright and free of battery rental issues, and would be LHD to boot.