Warning problems of the 2016 Subaru Outback

Since we've owned the car it has gone through 3 batteries and the blind site and lane assist go on and off all the time. Windows lock. Dealership said there is nothing wrong with the car. My mother is 80 and we have kept the car in the garage most of the time unless it's a grocery trip. She has called my uncle twice this year to boost her because the car wouldn't start. We keep the car on a slow trickle charge and it doesn't make a difference. How are we suppose to sell this?.