I have the driveway in one part with a serious slope. I played around with different weights and found that minimum in my case was extra 20kg. I have bought some gym equipment weights from Dechatlon sports shop here in EU. Was reasonably priced and it did made the snowblower the autonomous helper as it’s advertised. Without the extra weight it did cot stuck all the time because of the low clearance and because of the slope I have. Adding something that large to the back of the robot, then you also need to make new snow blowing maps again that the robot would have more room to maneuver without hitting things.
Before the added extra weight it was daily work for me to help it to get unstuck. I can now remember only one time this last winter I had to do this.
There is a post I wrote about this upgrade and you can see the picture here: