I have been away 6 months asked friend to turn car engine over once a week , now he told me car battery died over Christmas, so what I want to know if there is any damage done to the electronic systems.
The car is a 3 yr old Skoda Octavia (petrol)
Once the vehicle is started, either with a new battery (if the current one is damaged beyond use ... might be, considering the amount of time it was dead) or with the one which is in there already after it's been recharged, I doubt you'll see any issues with the electronics or otherwise. There are a few exceptions to this, one of those being if rodents have entered the picture and found insulation of your wiring as bedding material. As mentioned, the battery, having sit for so long, may have issues. You'll have to see if it will hold a charge. If you have a battery charger available, I'd try getting it up to charge with that, before starting the vehicle. Using the charging system in the vehicle will work, but a charger is a much better options for the battery and for the car itself.