The wagon started using more fuel after the battery was totally discharged due to a radio short 6 months ago.
Have travelled 10,000 km since.
Fuel consumption prior was 9 to 11 litres /100km after 13 to 15 litres per 100 km with the same driving patterns.

The computer should have re-learnt the settings by now!
Could a sensor fail due to the battery going dead flat for a week??

Any advice on where to start looking??

The only things that would have been reset from a week-dead battery would be the long term fuel trims that the computer stores over time.

Have you checked the usual things? Air filter, spark plugs, etc?

Oxy sensor could be off.

So many things to consider.

Does the car run a bit rough? When my alternator was playing up and flattened the battery it damaged the distributor and caused poor running. All better when i replaced the distributor.