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I have some of these lithium ion battery charging modules which are very commonly available online. They use a TP4056 charger and a DW01 protection IC.

The DW01 datasheet says that it should cut off discharge at 2.40 ± 0.1 V, which is already too low for my liking, but I've just done an experiment where this board allowed my 18650 cell to reach 2.2 V! I stopped the test manually for fear of harming the cell. When I provided charging power again, the board went into 80 mA recovery mode because the voltage was so low.

Through my reading, I've learned that due to voltage sag under load, batteries with a 2.5 V protection will bounce back up a bit, but I'd like to stop the discharge sooner.

I would like to prioritize the health of the cell, not squeezing every drop of current out of it. I don't mind stopping with 5% left. Can you provide any recommendations, pointers, or learning resources regarding protection methods with a shutoff closer to 3.0-3.3 V? Am I supposed to be using a different solution entirely, instead of relying on these "airbags"? I was not expecting this to be so challenging.

I have already read several dozen threads both here on electronics.se and on reddit. The consensus that I see time and time again is that discharging a cell below 3 V is not healthy for it, and yet all of these protection ICs are designed for 2.5 V. I can't make sense of the situation.

Davide Andrea
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voussoir
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  • Can you cheat with an additional diode drop or two to the sense pin? – winny Feb 17 '22 at 21:00
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    @winny Just to get this out of the way: I don't mind throwing these units away and buying different ones if there is anything that exists with the behavior that I want. I'm a noob at this and I don't have the proper judgement to know what cheats are safe and not safe. In fact, the TP4056 doesn't have power path management which is a feature I'd rather have in my charger. I have seen a few things about adding diodes, but there were downsides such as forward voltage being variable with temperature and also biasing the over*charge* detection in the wrong direction. So I'm not sure. Thanks. – voussoir Feb 17 '22 at 21:23
  • Sorry, but recommendations for specific products are off-topic for this site. – Elliot Alderson Feb 17 '22 at 22:09
  • Understandable. Hope you can find something which better fits your needs. – winny Feb 17 '22 at 22:17
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    @Elliot I was cautious about this in my phrasing. I'll accept pointers and learning resources in lieu of specific part numbers. At minimum, I'd just like to know if I'm totally on the wrong track and should be using a different means of protecting the battery than relying on the protection IC shutoff, since they all seem to be lower than what I want. Thanks. I have edited the question title to reduce the "specific product" problem. – voussoir Feb 17 '22 at 22:21
  • If the health of the cell is the priority, consider using a longer lived cell (LFP or LTO) but you'll have to look harder for protection circuitry adapted to them, or make your own. –  Feb 18 '22 at 13:35
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    The beauty of the TP4056 is that it does everything and does so cheaply. The counter side is that it made all the choices for you and you can't change them. If you want a BMS with customizable features, you will need to buy a fancier and more expensive one. – Davide Andrea Feb 18 '22 at 22:36

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