I meant that these ARE shrink wraps they sell separately for you to build your own packs....
Sorry, I didn't mean to imply you didn't make good packs, just offering info, since I have no way of knowing your level of expertise I covered all of what I thought might help
But if you've never seen them you should check out their assembled packs at least once. They must have some special equipment to do this... it's like a spot weld, almost no solder, great bar to battery contact. After sending a pack in to get checked out, I talked with them on the phone and got ideas how to do better on my own packs. I thought my soldering was fine before but
I saw a big difference in performance
and I have improved my own work also.