I like compliance, more travel with relatively constant force.
I haven't worked with these batteries. But they are a sandwich of some materials, each having a particular TCE. They will experience a range of temperatures. If anything in the sandwich expands with heat, either the spring system takes up the travel and maintains steady pressure, or pressure increases and something inside tries to get extruded. Alternatively, under cold conditions, they shrink and the pack falls out. (or vice-versa, depending on relative TCE rate of steel rods. vs. battery sandwich)
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How about doing just what you described, but with coil springs around each rod?
Suitably selected, they would be partially compressed when you reached the force desired.
One thing I really see in my yard is that PVC conduit expands, buckling into an "S" shape. Then contracts, pulling connections apart or breaking things. Much higher TCE than steel conduit and concrete wall it is mounted on.