[avar]

    > How do you even drain a 3.7V lithium
    > ion battery below 3.3V?

Connect the + and - terminals with an appropriately sized resistor, it'll drain all the way to 0V.

    > My devices that use 18650s will
    > not let them go below that.

Because you're not using the + and - terminals, you're using the + and - supply of a BMS, which is connected to those terminals. For this sort of testing you need to bypass the BMS, which'll have its own voltage cutoffs.

[quickthrowman]

I understand you can discharge a battery completely with a resistor, just like any other capacitor. I also know there’s a battery controller in my device.

My actual question should’ve been ‘Do people really use lithium ion batteries in devices without battery managers?’ I absolutely would not.

[avar]

Neywiny's comment upthread isn't that you should use these without a BMS, but that the review is relatively less useful because it's stopping testing at a relatively high voltage. E.g. if you search for "panasonic_ncr18650b.pdf" you'll find that Panasonic's own datasheets use a cutoff of 2.5v.

[Liftyee]

Some do. Anecdotally, some (uncommon, enthusiast-grade) flashlights I use don't have battery managers/over discharge protection, though most of mine do. If you can bear the responsibility of maintaining and storing the batteries properly, IMO there's no significant problems.