I have a 9 year old Dell laptop. The original battery made about 4 years and had 6 18650 Li-ion cells
I have had at least 4 replacement batteries since, all of which had 9 18650 cells.
3 of those generic replacements were lucky to last a year.
This latest one said it was a 'genuine dell' replacement and has indeed been the best replacement battery.
I have opened up the old batteries carefully and found usually one cell was quite poor, while the others would recharge and maintain 4.2 volts for a week or more.
But compared to a Panasonic NCR 18650b (3400mah), in my headlamp, they would last about 1/5th the amount of time. I basically quit bothering using them.
Th replacement batteries cells, those that I could find specs for, were 1800 to 1900 mah, when new.
Since it is usually just one cell which fails, a lot of cheapo packs are actually used cells, rewrapped and built into a new battery pack.
The 'genuine' Dell laptop battery was not much more expensive than the other brands which failed in short order, and while it has certainly retained its capacity much longer than all the other replacements, it could also be a 9 year old battery that was sitting on a shelf that whole time, as when i bought my first replacement, the 'genuine dell' was 4x the price of the one I purchased.