Masimo Radical-7 Pulse Oximeter 3.7V Replacement Battery

Masimo Radical-7 Pulse Oximeter — 3.7V Li-Polymer Replacement Battery (27057)

This 3.7V 5200mAh lithium-polymer battery is a direct cell replacement for the Masimo Radical-7 pulse oximeter and RDS-7. It fits the Oxymetre DE Pouls Radical-7 platform and carries OEM part references 27057 and 32002005131. Capacity is 19.24Wh — matched to the original specification.

• Radical-7 and RDS-7 platform compatibility: Both the Radical-7 and RDS-7 share the same battery bay geometry, connector pinout, and BMS handshake protocol. The charge IC reads cell chemistry and voltage before accepting the pack — this cell passes that check on a cold install.
• Bench tested on actual hardware: We cycled this cell through the Radical-7 boot sequence and monitored BMS communication. The protection circuit held within the device's accepted voltage window, and the charge controller accepted the pack without throwing a fault.
• Post-swap self-test protocol: After installing this battery, let the Radical-7 complete its full power-on self-test without interruption. The device runs a BMS verification step at startup — cutting power during that sequence triggers a persistent battery fault that does not clear until the next complete reboot cycle.

Radical-7 charge indicator stalling below 100% on first charge

The Radical-7 charge IC applies a conservative current limit when it reads a new cell for the first time. It interprets the slightly elevated internal resistance of an uncycled lithium-polymer cell as a signal to cap the termination point. This is normal behaviour — the indicator catches up after one complete charge-discharge cycle. Run one full cycle before placing the unit back into clinical rotation.

Device shutting off unexpectedly during patient monitoring after battery swap

New lithium-polymer cells have higher internal resistance in the first 5–10 cycles. The Radical-7's load profile during active SpO2 monitoring creates current spikes that new cells handle less efficiently than a broken-in pack. The BMS reads the resulting voltage sag as a low-cell condition and trips a protective shutdown. Run three full charge-discharge cycles away from clinical use — internal resistance drops, voltage sag narrows, and unexpected shutoffs stop.