Important to know, if you order this board

Bottom layer doesn't have any exposed copper. There are no solder pads or though hole components. Mention this in order details: "It is fine, if no exposed copper on bottom layer. Fill with solder mask ink.". If this isn't mentioned, engineers may halt the order and and ask for the missing solder mask layer.

This is exactly same version, which I ordered before

See the video below, where I tested this circuit. If there are any mistakes in the circuit in the video, they are in this version too. I'm not aware of any, though. Replicate at your own risk.

I don't have the design files anymore. Thanks to PCBWAY's "Share&Sell" -feature, I was able to share this project anyway, from "My Orders" -page. No updates are expected to this design, unless there is a whole new revision made from scratch (I don't have a need for that).

What is it?

It protects against overcurrent, overcharge and overdischarge.

Output turns off when overcurrent/short circuit is detected and returns back on when short is removed. When voltage of either of two cells drops below 2.9+-0.08V, output switches off and only returns back on after charger is connected.

What components it's based on?

This battery protection module is based on HY2120(-CB):

https://www.hycontek.com/wp-content/uploads/DS-HY2120_EN.pdf

Suffix of HY2120 is important! Different HY2120 versions have different fixed limits for protection features. For example some allow discharging to a lower voltage, than others and some have different behavior when short circuit is detected. Read the table found in the datasheet.

I used kia50n03ad -mosfets, which have on-state resistance in range of 10mOhm per mosfet, 20mOhm in total. Current sense voltage of HY2120 is 200mV, which means max current for this board is about 10A

Capacitors are 0603, resistors are 0805

Video