The cell library

The 12 cells this site will specify, with the figures a pack design actually depends on and a link to each manufacturer’s own datasheet.

A part number is verified or it is not here

A plausible wrong part number costs money and possibly a fire, so every entry links to the manufacturer’s datasheet and states which figures were confirmed against it and which are published typicals. One entry has no part number at all and says so, because there is no single datasheet to check a generic pouch cell against.

Capacity and current are a trade, not a ranking

The highest-capacity 18650 here takes under 5 A; the highest-current one takes 25 A and holds a third less. Neither is better. Which one is right depends entirely on the per-cell current your arrangement produces, which is why the designer computes that first.

Questions

What is C-rate?

Current expressed as a multiple of capacity. A 3 Ah cell at 3 A is 1C; the same cell at 15 A is 5C. It is the number that decides whether a cell is being used gently or punished, and the rating that matters is the one on that cell’s own datasheet rather than a rule of thumb.

Do you recommend where to buy cells?

Not currently. Every cell page links to the manufacturer’s datasheet and nothing else. If supplier links are ever added they will be disclosed on the page, and the ranking will still be computed from electrical fit alone — a designer that recommends the cell paying the most commission is worthless, and it would look exactly like one that does not.