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.
http://www.instructables.com/id/DIY-Constant-current-load/
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?
Thanks!
Best Answer
CR2032 batteries are simply not intended for high current. They are lithium/MNO2 chemistry, which makes them lithium, not lithium-ion. For the behavior of a reputable source, see here, for instance where pulling a pulsed load of 23 mA produced about 1/2 volt drop in the output voltage. With that said, your nominal 37 mA isn't that much greater, so I'd expect something on the order of 5 hours duration for your test.
You need to test at much lower currents, like 1 mA max, and take your time. Your nominal 2200 mA-hr would last about 9 days at 1 mA, but even this is stressing the battery. From the web page, a 100 ohm load (about 3 mA) will pull down the battery voltage by half a volt in a few seconds.
EDIT - As Ecnerwal has pointed out, the battery was rated for 220 mA-hr, not 2200. My bad - brain fart. As a result, I'd expect something on the order of an hour or 2 for 37 mA, so low-current testing is still a good idea. At 1 mA, 220 mA-hr is 9 days, of course.