About this replacement
Sunmi V1 — 7.4V Li-ion Replacement Battery (W5900 / W5600)
This 7.4V, 5200mAh Li-ion battery replaces the original power cell in the Sunmi V1 portable POS terminal. It fits units carrying OEM part numbers W5900 and W5600. The Sunmi V1 is a handheld payment terminal used in retail, hospitality, and mobile merchant environments.
- V1 platform fit: The W5900 and W5600 share the same physical form factor, connector pinout, and BMS handshake protocol on the Sunmi V1 board. Both OEM numbers reference the same cell pack architecture, so this replacement covers both variants without modification.
- Bench tested on actual hardware: We cycled this battery through the Sunmi V1 boot sequence and simulated transaction loads — including receipt printer motor draws and simultaneous wireless activity. The BMS held steady through multi-peripheral draw spikes without tripping overcurrent cutoff.
- First deployment tip: After installing this battery, run one complete transaction cycle — from boot through a live payment — before deploying in a high-volume shift. The V1's charge management IC maps cell capacity during normal operation and needs at least one full power cycle to display an accurate charge indicator.
Why the Sunmi V1 reboots mid-transaction after a battery swap
The Sunmi V1 pulls a combined load from its display, wireless radio, and thermal receipt printer at the moment a transaction completes. On a fresh cell, the BMS has not yet profiled the battery's internal resistance, so it applies conservative overcurrent thresholds. A printer motor start-up spike can push instantaneous draw past that threshold, triggering a protective BMS cutoff that looks like a reboot. Running two or three full transaction cycles — including receipt prints — lets the BMS recalibrate its trip point against the actual cell characteristics and stops the false cutoffs.
Terminal not powering on after sitting unused in storage
Li-ion cells self-discharge at roughly 2–3% per month. A Sunmi V1 left in a drawer for several months can arrive with a cell voltage below 3.0V per cell — the point where the BMS locks output to prevent damage. The terminal will show no response to the power button. Connect the terminal to its dock or USB-C charger and leave it for 20–30 minutes without pressing anything; most BMS circuits enter a trickle recovery mode that brings cell voltage back above the 3.0V unlock threshold before resuming normal charging.