I'm jumping into this thread, because I have just disassembled a 12v battery pack, in use for about 3 years, and I have found that all 4 cells are significantly swollen after that time. It was a foam compressed battery pack; the foam was both very tight AND quite ineffective. The outer case was plastic, and maybe allowed some expansion of the outer case as well. When I set the cells down on a solid table and push them together, there is a gap of about 1/16 between adjacent cells. This gap appears in both of the side joints, and also along the top. It is due to cell expansion, with the largest "bulge" present in the middle of each cell face.
Although their total lifespan is significantly compromised already, these cells are still good. I have disassembled to replace a failed BMS, and I will be rebuilding it with compression springs. In this case, foam was unable to provide the hundreds of pounds of compression which the battery packs required. The cells are 6.5 inches tall and 7 inches wide, so I have calculated a force of about almost 300 lbs on those cell faces (6.5 * 7 * 6 PSI = 273 lbs), increasing as the cells become highly charged. Without steel rods and compression springs on two very solid end plates, it seems impossible to achieve.