About this replacement
Sigma SW-11UVA — 7.4V Li-ion Replacement Battery (XC-2S-10)
This is a 7.4V 1000mAh Li-ion battery for the Sigma SW-11UVA pulse oximeter. It replaces the original XC-2S-10 cell that powers non-invasive SpO₂ and pulse rate monitoring in clinical and home settings. When the original cell degrades after repeated charge cycles, this replacement restores full device operation.
- SW-11UVA platform fit: The SW-11UVA uses a 7.4V two-cell Li-ion configuration with a specific BMS handshake tied to the OEM connector pinout. This cell matches that voltage rail and connector geometry so the device BMS communicates correctly with the replacement pack.
- Bench tested on actual hardware: We cycled this battery through the SW-11UVA's charge and discharge sequence and confirmed the BMS accepted the cell, completed charge termination cleanly, and held voltage through a full measurement session without triggering a low-battery interrupt.
- Post-swap self-test protocol: After installing this battery, let the SW-11UVA complete its full power-on self-test without interruption. The device runs a BMS verification routine at startup — cutting power during that sequence can register a persistent false battery fault that won't clear until the next clean reboot.
Why the SW-11UVA alarms low battery immediately after a confirmed full charge
The SW-11UVA's BMS stores a learned capacity profile from the original cell. A new replacement cell has a different internal resistance signature, and the BMS misreads it as a partially depleted pack on the first cycle. This is not a fault with the replacement battery. Run one complete charge-discharge cycle before relying on the battery indicator — after that cycle, the BMS recalibrates its threshold to match the new cell's resistance curve and the alarm clears.
SW-11UVA fails to power on after the replacement battery sat unused in storage
Li-ion cells self-discharge during storage. If the cell voltage has dropped below approximately 2.5V per cell (5.0V at the pack level), the SW-11UVA's BMS will not initiate a charge cycle — it reads the pack as unsafe and blocks startup entirely. Place the battery on charge immediately after receiving it. Most charge ICs will apply a low-current pre-charge trickle at this voltage level; leave the device on charge for at least two hours before attempting to power on.