I don't foresee mounting it more rigidly to be a problem.
Here's a few ideas:
1. Buy a larger battery to fill the hole in the oil tank so it can't move around as much.
2. If a larger battery isn't possible you could use a rigid foam to fill the void in the oil tank to prevent movement.
3. Cover the terminals so if something does contact it will not create a connection. My 2005 Ultra has caps over the terminals.