This is the kind of test I did on my VTC4 as an exemple....
The cells I got were around 20.9 milliohm DC internal resistance (VTC4 are very low resistance, even a little more so than the VTC5 but still very close).
You can see I used different 100W resistors as dummy loads...
I also simultanously measured voltage and amps.
My cells were initially close to 3.964 volts (float voltage).
I tried different resistors (big 100W ones.... otherwise they burn) : 0.5 ohm, 1 ohm, 2 ohm, 4 ohm
At 0.5 ohms, I could pull close to 7 amps ! and that would drop voltage from 3.964 to 3.818 V
See what I mean ?
If it drops from 4.20 Volts to 3.0 Volts at 10A in just a few seconds, it's obviously a fake.
If it only drops from 4.20 Volts to 3.80 or 3.90 V at 10A for a few second with the load resistor across the cell, it's looking good.
Remember.... don't leave it too tong of you will just discharge the cell... and voltage will go down with discharge state.
On a fully charged (4.20V) VTC5 cell, at 10 A, the voltage at 10A load shoud be : 3.7 volts after 3 minutes discharge ; 3.5 Volts after 6 minutes discharge ; 3.35 volts after 9 minutes discharge ; 3.2 Volts after 12 minutes discharge ; 2.8 volts after 15 minutes.
That's if you maintain the load at 10A constant the whole time (in reality, the amp load will go down with the voltage a bit).... Upon removing the load resistor, the 2.8V shoud jump back to 3.25V no-load (study that discharge curve to understand... see my preceding reply above).
In brief, I call this the "Load-test" method for spotting fake "High Power", "High Drain" or "High amperage" cells.
The VTC5 is one of those "High Power" cells....
For testing Low power (but high capacity) cells (ex : cells rated for 5amps max), than I suppose checking capacity if a better way to spot fake, as opposed to doing a "Load-test".
Let's say you test a high capacity Panasonic NCRB cell that's good for 5 amp current or so but can give 3300 mAh capacity at 0.1C, well the fake or cheap laptop cell can also give that 5 amp current, but it will only probably yeild 2200 to 2600 mAh capacity, in which case, testing for capacity is the best way to tell if it's a fake or a real genuine Panasonic NCRB cell.
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