You will never find decent specs on Ebay, Amazon etc. Go to the OEM site in China.
Only use brands certified by major companies.
Never assume ESR to be constant over 500 cycles unless specified. Never make any assumptions for that matter, unless verified.
XTAR quotes <=11 mohms for the 21700 with Ic=4A max
I would not expect the charge rate to increase with battery size due to temp rise of the inner most layers may increase with cell diameter, even though AH and ESR can improve. So do not expect any improvement, and in fact derate ESR for larger cells until proven otherwise.
https://www.xtar.cc/product/INR-21700-4200-High-drain-Li-ion-Battery-120.html
other
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Beware of partial dentrites and know how they are detected, created and hopefully screened out at factory.
ESR is the bottom line that when it has a NTC and sufficient energy transfer beyond Imax and above Tmax can trigger a thermal runaway event. Thus higher ESR means higher safety risk.
ESR is also a quality measure or Figure of Merit, FoM that correlates with cell size or diameter, Parallel Np arrays and weight of each cell. Quality varies with Process Design improvements and Cost Reductions which will be in constant change till the next generation.
ESR is an indicator of aging and State of Charge (SoC) and temperature if other variables are constant.
ESR can be estimated from max current ( assuming some temp rise and power thermal resistance and max temp) or from max charge rate relative to Ah capacity.
In the end if you intend to buy alot, you will have a DVT plan and qualification process and have a safety margin and/or thermal sensor in your design.
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