I recently bought a lot of cheap CR2032 batteries from aliexpress. Since there is no manufacturer stated on the package or the batteries, I would like to know if these batteries really have 220 mAh or are they as fake as they are cheap. I would like to use them for a project with the bluetooth SoC nRF51822 QFAA, which draws 3 uA in sleep and few mA when radio is active.
I made a constant current load, to draw the constant current over time and to calculate the total capacity, but I was unable to determine the correct capacity because the voltage on the battery went down to 0.1 V and current from the battery to 10 mA. I used this schematic from instructables.
I changed the resistor to 10 ohm (around 11) and the voltage on the pot to 0.5 V (not exactlly 0.5V). With these calculations, I should have gotten 45 to 50 mA constant current, but when i measured it, it was 37 mA (good enough). But after a while (no more that 30 minutes) the current dropped to 10 mA and voltage to 0.1 V. After disconnecting the battery the voltage slowly raised to about 3 V. The same happened with the Chinese batteries and with some of the known battery brands.
Is there any other way (or a better schematic) to test CR2032 battery capacity, without buying some kind of battery measuring equipment??
Why did the voltage drop? Was it because of the "high" current I was draining?