@matthewslack 's points are valid ones but depending on the physical structure of the battery, it might be possible to remove it from the hard case and cover it in shrink wrap instead.
The hard case clearly offers protection to the battery but that doesn't necessarily mean that the battery isn't adequately constructed/protected when out of the hard case. I mean, many an enthusiast has built their own battery pack and NOT mounted it in a hard case but something like a padded frame bag or saddle bag.
The big question is, how do you the OP, determine that the pack is suitable for using outside of the hard case? It would help if you've successfully built your own battery packs as the presumption would be that you by virtue of that experience, have a good knowledge of what constitutes a sound and safe pack build.
Without that knowledge and then removing the pack from the hard case and using it in a saddle bag, is venturing into the unknown and should not be taken lightly.
If you are willing to take the next step and you feel confident in removing the battery pack from the hard case, then you'll be able to go some way in determining the pack's structure and posting pics on here may illicit useful comment.
Maybe start with a youtube vid of folks building battery packs to at least get some idea as to what folks do to ensure a sound build. You could start with this one
HERE by ebikeschool.com (Micah Toll) and many of his other videos.
