I see lots of comments about cold soldering or difficulty do it right.
I tossed my impact crimper 40 years ago due to terminal damage. Squeezing should only be done on brand new copper penny bright copper wire.
Try a hair dryer set on high to shrink the shrink tubing -- until the adhesive lining oozes out.
A basic LAW about how is solder is flat out dead wrong. When a tip is heating the work, a droplet of solder should be hanging from the soldering iron tip. Terminals BLUSH as they pass the point where solder will melt.
A correct solder joint has a glossy appearance
A cold soldered joint looks like dried aluminum paint.
Gross and I mean GROSS overheating of the work would damage wire insulation. I use a Harbor Fright refillable mini torch. Orange and Black. It has a w-i-d-e base for stability. Using a full size propane torch even on the largest battery lugs is a chore. A cheapo HF heat gun is world's easier to use. A torch sunburns red shrink tubing butt-ugly
