Practice makes perfect,ive been soldering for a few years,but i buy battery packs pre-made ,just cause of the hassle of doing them yourself,But this is a hobby and it is nice when you Do/Make/Build something on you own,i have repaired a few 4.8V's that i use for my Super Cub,the tabs were already on the battery and its alot easier.

PS you learn from your mistakes lol