My experience has been that the frequency is rather low at the beginning of the game. The deeper you get into the game, the higher the frequency. I have a game in the 180s right now, and if I don't save and exit every 4 battles or so, I'm likely to get a post-battle crash.

You can get around this by frequently saving, exiting, and restarting. It's a pain, but it helps you avoid the problem. In that game in the 180s I mentioned earlier, I've had very few crashes.