This is an enhanced USB-powered lithium ion polymer battery backup charger that can power a load from USB. When connected to USB power, the USB voltage is connected to the board's OUT+ and OUT- conenctors and can be used to power your device. It also charges a battery by connecting the battery to the B+ and B- connections. It automatically switches to battery power when the USB connection is removed, in turn powering your device from the battery.
The module uses a TP4056 charging controller with a DW01A Lithium-Ion battery protection IC to protect the battery. It provides 1A charge current then cuts off when the battery is charged. Furthermore when the battery voltage drops below about 2.4V, the protection IC will switch the load off to protect the cell from running at too low of a voltage - and also protects against over-voltage and reverse polarity connection. However please check you have it connected correctly the first time. An LED indicates power/charge/battery status.
This module is perfect for charging single cell 3.7V 1 Ah or higher LiPo cells such as 16550s and 18650s that don't have their own protection circuit. It can charge two cells in parallel, however since the two cells share the charging current, they take twice as long to charge as a single cell.