To give a background on this, I have been running tests to determine the actual lifespan of a 3 cell pack of some Samsung 18650s and Tesla 2170s at just above freezing. The Samsungs are INR18650-35E and the Teslas were pulled from a 2018 Model 3. Voltage was checked on all cells before being wired together with a BMS connected to them. This one.
These cells were placed in a cold environment, around 35F and then connected to the LED strip and left to run in front of a timelapse.
In between the cells and the LED strip was a watt meter/power analyzer, I bought it from Amazon here.
The Voltage dropped from a full charge to 9.0V as expected and then cut out. However after harvesting the data, I noticed something odd. The life of the Samsung 18650s in my test lasted about 7.5 hrs. The amp and watt pull slow decreased over the course of the first 4.5 until they hit 0 (although the LEDs didn't turn off), and then rebounded back up to to their initial pulls at the start of the test and then slowly receded until the BMS cut them off.
Any ideas why this would happen? The same thing happened with the Tesla 2170s too, just after over half their capacity was used.