About this replacement
Sunmi V1 — 7.4V Li-ion Replacement Battery (W5900 / W5600)
This is a 7.4V 6400mAh Li-ion battery for the Sunmi V1 point-of-sale terminal. It fits the compact V1 handheld used by merchants at the counter and on the floor for payment processing. Replaces OEM part numbers W5900 and W5600.
- V1 platform compatibility: The W5900 and W5600 share the same voltage rail, physical footprint, and BMS handshake protocol on the Sunmi V1. Both part numbers are interchangeable within this terminal generation.
- Bench tested on actual hardware: We ran this cell through full boot cycles on the V1 and confirmed the BMS handshake completes correctly. The charge IC accepted the cell without triggering fault flags, and the thermal sensor reported within normal range under combined display, wireless, and printer load.
- First-use calibration on the V1: After fitting this battery, run at least one complete transaction cycle before deploying in a live environment. The V1 maps capacity during normal operation and needs one full power cycle to calibrate the charge indicator. Skipping this step can cause the charge display to read inaccurately during the first shift.
Terminal rebooting mid-transaction after battery swap
When the V1 receipt printer fires, it draws a sharp current spike that can briefly exceed the BMS overcurrent threshold on a new cell that hasn't completed its first charge-discharge cycle. The BMS interprets the spike as a fault and cuts output, causing the terminal to reboot. This typically stops happening after one or two complete charge cycles, once the BMS has profiled the cell under real load. If reboots continue past the second cycle, check that the battery connector is fully seated — a partial connection raises contact resistance and worsens voltage sag under the same spike.
V1 not powering on after sitting unused in storage
Li-ion cells self-discharge over time, and if a terminal sits unused for several months, the cell voltage can drop below the BMS recovery threshold — typically around 2.5V per cell, or roughly 5.0V at pack level for a 7.4V 2S configuration. At that point the BMS locks output and the terminal will not respond to the power button. Place the battery on a known-good charger and leave it connected for at least 30 minutes before attempting to power on — most chargers apply a trickle recovery current below 3.0V per cell to bring the pack back to a chargeable state. If the charger shows no activity after 30 minutes, the cell has likely dropped below the recovery floor and the pack needs replacement.