TysonScott said:
I found these cells and they claim 3.6v 90ah 6c continuous and 12c peak, at a affordable price with free shipping. What do you guys think about these? should I expect claimed specs or is it a scam? price seems good but still reasonable.
This image
https://ae01.alicdn.com/kf/S92f55700a3524fc4af2489c2ae731edfl.jpg
S92f55700a3524fc4af2489c2ae731edfl[1].jpg
shows a cell that appears to have a similar volume to the 20Ah EIG C020 NMC cells I'm using. Despite my cells being perhaps a 15-year-old design, I cannot imagine they've improved capacity capabilities enough to get 90Ah out of that same space. So I must be misjudging the size; perhaps they are a lot thicker.
They give a weight of 1.16kg, while the EIG cell is only 428g, so it's three times the weight, which implies at least three times the capacity.
I don't see any dimensions, though, so can't compare those for more confirmation, and there is nothing in any of the images that can be used as a reliable scale.
The C-ratings sound perfectly plausible for a cell this size and low resistance....
The resistance itself...dunno. The EIG cells are rated at <3milliohm, but have very similar C-rates, I would expect higher C-rates for a cell with less than 1/3 the resistance.
The big problem most of the cells people buy from typical sellers is the cells have a wide spread of characteristics, so the resulting pack built from them has significant variation between each seriesed cell (or cell group), and that means they don't perform the same as each other, so they don't stay balanced over time without a device (BMS, etc) to do that at least periodically. They also don't sag in voltage under discharge equally, so the lowest-capability ones will cause the system to cutout or underperform sooner than the rest.
Buying a single cell (or even a couple) won't tell you anything about that part, even if the individual cell(s) test great, and within their specified limits. You'd have to have at least enough of them to build your pack from, and test them all for behavior and characteristics under sufficient load to be similar to your conditions, to know for sure that they'd behave as required.