I made a save when I had a ransom demand so I can test out a few tactics. The raiders were split between two locations that I could tell, and I didn’t notice the 2nd location until I went with my test. The test was to wait until the winter storms before denying them so I can see if they are affected by the cold. It seems they are not but I’m not sure that is a bug. During this event, I got word of a building being attacked that was on the other side of town. Here I could see the battering ram and I decided to load from my save six months prior and check out my options for defeating that.
The load ended up making the game run really slow, and as it turns out, the battering ram went to town on my wall early and then started aiming for guard towers. I had to set a bunch of villagers on it. In my first test, I tried to let loose the soldiers in the barracks against a formation of raiders but they would not attack them, even if explicitly told to do so. At the very least, I figured this would trigger an automatic deny response to the ransom and start the battle. To my surprise, the battering ram could still be attacked while delaying on any response to the ransom, but probably because it was already engaged as an attacker.
I can’t be certain at this point if this is a bug from reloading the save, or if the battering ram will always attack without waiting, but since the first round it didn’t hit my wall until six months later when I clicked deny to watch how the storm affects the raiders, I’m assuming that in the first round before reloading, the battering ram did not attack.