I have an aging Gateway NX560XL laptop. The battery is toast and a new one, even aftermarket, starts at $130. So, to experiment, I began tearing apart the old battery to see what can be done. I found it used 8 standard size 18650 Li Ion cells arranged two cells parallel then in series (like: ====). Some online shopping revealed ~$7-13/ea replacements depending on mAh output. My plan is to load test to determine the bad cells and replace only those, as I read that typically only 1 or 2 may be bad.

I'm proficient with soldering, however these cells are attached with welded tabs. Some of them broke during disassembly and I'm not sure how to reattach them. What I found online are cells like these that have solder tabs pre-welded to the ends so I can solder wires onto.

Is there any guide available that provides the instructions and parts to do this kind of rebuild?