Sorry if this has already been asked, I tried searching but might not have the right vocabulary.
I'm starting to use lithium-ion batteries to power projects, and I've wound up with some 18650 cells. Not wanting to use unprotected cells, I hooked them up to some common and cheap TP4056 charge/protection boards. This lets the batteries charge up to 4.2V easily, but I've read that the undervoltage protection on these boards is really more of a failsafe than a way to keep the battery healthy; it doesn't cut off until 2.5V, which I'm worried might damage the cells pretty quickly.
It looks like there are affordable over/undervoltage protection ICs for li-ion batteries, but the highest undervoltage cutoff I can find is still only 2.8V on something like TI's BQ29700.
So here's my question - if I want to err on the side of caution when draining the batteries, can I use a 'low voltage supervisor' IC hooked up to an N-ch MOSFET as a cheap/simple extra layer of protection to cutoff at something like 3-3.5V? Would I be better off just using an opamp? Is the voltage supervisor's 3uA enough to continue draining the battery appreciably?
Here's what I'm thinking of specifically - it's just a high-side N-ch switch with its gate attached to the voltage supervisor's "reset" pin, which is pulled low during undervoltage in the MIC2776L model:
And here are the non-discrete parts; I tried to pick a MOSFET with low on-resistance:
Adjustable low-voltage supervisor - MIC2776L: http://ww1.microchip.com/downloads/en/DeviceDoc/mic2776.pdf
N-Ch MOSFET - PMV20EN: https://assets.nexperia.com/documents/data-sheet/PMV20EN.pdf
Thanks! And sorry if I'm missing something, I'm pretty new to this.