Capacity grading, matching, welding, fitting the BMS, heat-shrink wrapping — five steps. For the welding step I used the UK1, 0.15 nickel-plated at gear 60, just right for full penetration. The one thing I most want to say: matching matters ten times more than welding. If cells from the same batch differ by more than 5mΩ in internal resistance, no amount of good welding afterwards will save it. The most-asked question in the comments, "how much per pack?", is answered too — in step 4 of the project.