The Li-ion 1S BMS (Battery Management System) battery charger module is based on the TP4056 chip. The TP4056 sets the charge, battery over-charge, over-discharge and over-current protection, all in one small module. Input power is provided via the on-board USB  connector or 5V input soldering pads. Charging status is indicated via on-board LED’s.
This is an enhanced USB-powered module for charging rechargeable lithium batteries using the constant-current/constant-voltage (CC/CV) charging method.

The device to be powered by the battery is connected to the module's OUT+ and OUT- connectors and the battery is connected to the B+ and B- connections. When connected to USB power, the module provides up to 1A charge current until the battery is charged, then switches to a constant voltage mode to keep it charged.

During use (when USB power is disconnected), if the battery voltage drops below about 2.4V (over-discharge), the DW01A protection IC disconnects the battery from the OUT connectors, disabling discharge to protect the battery from running at too low of a voltage and to protect the device being powered from an under-voltage condition.

When the module is then connected to USB power, it will trickle charge the battery to 2.9V (the over-discharge release voltage), at which point the charge current will be linearly increased to 1A maximum and the module will reconnect the battery to the OUT connections, allowing discharge of power from the battery to a connected load. Although the module cuts output power from the battery during an over-discharge situation, it still allows trickle charging of the battery to occur.

The module also protects against overcurrent and short-circuit protection. It will cut the output from the battery if the discharge rate exceeds 3A or if a short-circuit condition occurs.