Dual Function: 1) Charge lithium cells from a 5V power source 2) Protect battery from over-discharge and over-currentCharge input: 5V DC • Maximum charge current: 1000mA • Charge cut-off: 4.2VDischarge protection cut-off: 2.5V • Over-current protection cut-off: 3AMicro-USB input • Size: 2.6×1.7cmThis is an enhanced USB-powered module for charging rechargeable lithium batteries using the constant-current/constant-voltage (CC/CV) charging method.This module provides constant-current/constant-voltage (CC/CV) charging, along with protection against over-voltage, over-discharge, over-current and short circuits to protect the battery and the device that it is powering.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, if the battery voltage drops below about 2.4V, the DW01A protection IC disconnects the battery from the OUT connectors, disabling discharge to protect the battery from running at too low and self-destructing.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.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.