Cell selection

Electrochemistry 102 (DIY Battery 102)

Generally, for most NMC Li-Ion Cylindrical cells, you have 3 types: Example cells are all 21700, but same logic applies for 18650s and generally most rechargeable LIBs.

1. High Capacity, Low discharge rating, Cheap cells. (5Ah, 1~2C C rating) High IR of the cells (hence low C rate)

Ex: M50 Variants, Samsung XX(Number)-E Variants

2. High/Low Capacity, Slightly higher discharge rating (than group 1), Slightly more expensive cells than grp 1. (4~5Ah, closer to 5Ah, 1.5C~3C Rating) Slightly lower IR than group 1 cells.

Ex: M50LT (latest M50 variant), Samsung G/S Variants.

3. Low capacity (on 4Ah Ballpark range), High discharge rating. Expensive. Low IR of the cells. about half of group 1s, but refer to your datasheet.

Ex: Molicell (P42A, P45B)

Use case: Use Cells on Group 1 for high capacity packs that won't get lot of continuous load, around 1~1.5x of their Amp-hr rating.

Group 2 cells are for balanced uses, but should still be avoided for heavy C rating uses (above 2C)

Group 3 cells are basically "Throw money at your problem" solution to cell selection. most expensive, but will do the job. High C rating design packs require extra busbars to reduce IR of the battery. Calculate resistance of metals