China is a magical place where you can get everything for a fraction of a price. Like 10000mAh 18650 LiIon batteries for $1.5. Of course, we have to begin with a note, that there are no 10000mAh 18650 batteries! Technology does not allow for such energy density. And if they would exist, they would not cost $1.5. Closer to $15. Anyhow, I’ve bought a couple of cheap 18650 on Aliexpress and tested them with a DIY OpenSource OpenHardware Arduino-based battery discharger.