4000mAh UPS Expansion Board with Lithium Battery — Portable Power & Indoor UPS Protection

This expansion board includes a 4000mAh lithium battery and supports two distinct operating modes: outdoor portable power and indoor UPS. In outdoor portable mode the motherboard runs solely from the onboard lithium battery; the maximum external power supply capacity is 5.1V 2.5A. For indoor UPS operation, plug a Micro-USB into a standard 5V 2A power adapter — the external USB-A output can deliver up to 5.1V 3A. A 4+2LED indicator provides charging/discharging status and a visual battery power display. The board integrates overcurrent and over-discharge protection. The external output port features a self-recovering protection to prevent damage from external short circuits: if the combined current of the two USB output ports reaches 3A the self-recovery will trip, and when the external port returns to no load the 5V output automatically restores. PMU over-discharge protection is also included — when the lithium battery voltage falls below 2.8V the PMU detects over-discharge and automatically cuts off the 5V output.