This document will go over my considerations for which cells to purchase in sample quantities to test before bulk purchasing cells. Here are the main questions I had going into this investigation.
How many cells of each brand should we purchase?
Which brands should we purchase?
Should we purchase both 18650s and 21700s or just 18650s?
How many cells of each brand should I purchase?
There isn’t really a good answer for this question, basically the more cells we have the more accurate our findings. Based on our budget for the sample purchase, we can have 4 * 12 cells or 3 * 16 cells.
Which brands should we purchase?
We should ONLY purchase from reputable large brands as they mass produce their cells and have less defects.
Someone did tests on the big 4 companies,https://secondlifestorage.com/index.php?threads/3500mah-cells-tested-sanyo-vs-panasonic-vs-lg-vs-samsung.4948/
the results are that Sanyo and Panasonic are the best, with Samsung in third place and LG being a league below.
Maybe it would be okay to buy Sanyo, Panasonic, and Samsung since we already have some understanding of LGs. Need to look more into this.
Should we purchase both 18650s and 21700s or just 18650s?
Purchasing only 18650s would make testing simpler.
21700s may be cheaper and make a more energy dense pack? https://cmxbattery.com/lithium-polymer-knowledge/advantages-of-21700-battery-cell-with-18650/ Although discussions on solar car reddit makes the benefit seem negligible. https://www.reddit.com/r/solarracing/comments/djql53/panasonic_vs_sanyo_18650s/
Should do some hand calculations to verify this.