here is a true Chinese knock off and no guesses what it is at all. I was sent 10 of them as a joke by a friend in a bag marked Tofu transistor.

 

ε = I·(r + R) = v + V -- where ε is EMF of the galvanic cell , r is the equivalent internal resistance of the galvanic cell , I is the current through the series circuit of battery and resistor R.
-- at your case --
ε = I·(r + Rꜱ + R) = v + u + V -- where Rꜱ is 100mΩ , u is the voltage drop at Rꜱ , which value must be pre-calibrated for different currents at different ambient , R includes the non-linear channel resistance of the MOSFET which also is T° dependent and current dependent . . . but also the r is dependent on SOC of the battery & rate of discharge of the battery & possible PWM/PFM frequency and duty

. . . basically you never mentioned what you hope to achieve with your experiment ???

It's not exactly an experiment. it is or will be a part of an even larger more insane project I have been working on for I could say since I was a teen and that would be true but the teen me had no chance of bringing it to life I at least have a chance to do it. and it's exactly what I want or will be.

 

here is a true Chinese knock off and no guesses what it is at all. I was sent 10 of them as a joke by a friend in a bag marked Tofu transistor.

It's readily apparent that the device was black topped.

This is a slide from a NASA presentation on counterfeiting in China:

 

I ordered the AO3400's and the 3401's I got 10 of each

I just remembered that AO3400 and AO3401 have been obsolete for a while now. The replacement for AO3400 is AOSS32334C. Specs for the replacement are better; except that threshold voltage increased by about 1V.

Where did you order from? I was tempted to buy a reel of each from AliExpress when they were end-of-lifed, but decided not to tempt fate.

Counterfeit components in Shenzen China:

 

ε = I·(r + R) = v + V -- where ε is EMF of the galvanic cell , r is the equivalent internal resistance of the galvanic cell , I is the current through the series circuit of battery and resistor R.
-- at your case --
ε = I·(r + Rꜱ + R) = v + u + V -- where Rꜱ is 100mΩ , u is the voltage drop at Rꜱ , which value must be pre-calibrated for different currents at different ambient , R includes the non-linear channel resistance of the MOSFET which also is T° dependent and current dependent . . . but also the r is dependent on SOC of the battery & rate of discharge of the battery & possible PWM/PFM frequency and duty

. . . basically you never mentioned what you hope to achieve with your experiment ???

I would call an 18650 cell with an internal resistance of 100+mohm an end of life cell. most that I have worked with have ranged between 30 and 50 mohm new off the shelf after a time of normal and sometimes heavy use that internal resistance can and does change it climbs at about the same rate as the capacity is lost. we made specialized cells for various mining and scientific power needs. some of those battery banks were expected to deliver on demand upwards of 300 amps and those we saw go on the bad side much quicker and there was little we could do about it. but that department was never my area we had smart engineers mostly working in that department my job for a couple tears was burning out 18650's and 21700 cells and report on my findings and suggestions for better battery packs for the heavy draw current battery banks. is 21700 better than 18650 for that purpose and which would offer better longevity. from then it was up to those smart engineers to take over and ahhm make it happen.