Clamping something without compliance that is going to expand is like freezing a glass bottle of water that doesn't have any air in it. Enjoy picking the glass shards out of your freezer.In another thread I implied that the torque we're looking at is so small that the margin for error is large, meaning that A) confidence levels are questionable and B) it doesn't take much to be off. Of course, I was talking about the torque on the terminals, but now I'm thinking the same thoughts may be appropriate for clamping.
Get the compression snug enough that you can lift the battery by the threaded rod with no cells falling out. If a cell falls out, it's too loose.
Springs provide both compliance and an easy way to set the preload. Both of which are absolutely required if you intend to do this.