As the battery is nearly new it will hold it's charge for a long time, if you started it and let it run for 20 minutes that would not be enough to charge the battery up to the level it was before you started it .
Also condensation would gather in the engine and exhaust pipes.
You must have a friend who is insured to drive their car, ask if he/she is insured to drive a car not belonging to them, most comprehensive insurance policies do provide that sort of cover.
If you have a friend like that he/she could take you for a drive of 30 miles or so every 6 weeks or so that would free everything up in the car.