Youmile 10PCS 1S 3A 3.7V Lithium Battery Protection Board 18650 Charger Module BMS PCB Protection Board for Li-ion Lithium Battery Cell with Nickel Strip

After buying some charge controllers which are suposed to have this feature built in, Sadly damaged a few batteries finding out the hardway, anyways these lithium protection boards saved the day as they do indeed shut off the battery if they become low, completly isolates the battery with very little current draw, a must have for tinkering and makers who use lithium cells in projects, this little device will save your cells from damage and seem to work very well.

If the battery you are charging is <3.4v the current draw is way above safety levels >3A for 3000mAh. As I use a variable lab PSU to charge the batteries I restrict the current to 2A max which is ok.These seem to work fine in normal applications and cut off charge as the battery voltage approaches 4.1V (max charge).Warning - If you are charging Lithium ion that have been idle or in storage for a long time I would recommend slow charging them manually until they reach +- 3.4v. Otherwise the current draw will exceed mAh/2 current nominal.

works as expected

I was expecting these to be about a similar size to an 18650 cell and I was shocked to see how tiny they were. They seem to work ok.