Masimo Radical-7 9500 Compatible Battery 3.7V 3750mAh

Masimo Radical-7 9500 Touchscreen — 3.7V Li-ion Replacement Battery (P1247900079)

This 3.7V, 3750mAh Li-ion battery replaces the original cell in the Masimo Radical-7 9500 Touchscreen pulse oximeter. It also fits the broader Radical Pulse Oximeter series, including units listed under OEM part numbers 23794, 25950, B11939, and P1540000019. The Radical-7 monitors blood oxygen saturation and pulse rate in clinical settings, so a functioning battery is non-negotiable.

• Radical-7 series compatibility: These models share the same single-cell Li-ion architecture, connector pinout, and BMS handshake protocol. Swapping between Radical-7 variants requires no adapter or firmware change — the battery management system authenticates using the same cell chemistry profile across the range.
• Bench tested on actual hardware: We cycled this cell through the Radical-7 boot sequence and confirmed the BMS completed its internal verification without triggering a fault. Charge acceptance was normal from the first cycle, and the protection circuit responded correctly to load draw during simulated monitoring sessions.
• Post-swap startup protocol: After installing this battery, let the device run its full power-on self-test without pressing any buttons or interrupting the sequence. The Radical-7 BMS runs a chemistry verification at startup — cutting power during this phase logs a battery fault that won't clear until the next complete reboot.

Why the Radical-7 triggers a low-battery alarm with a fully charged new cell

The Radical-7's BMS uses a learned capacity model to calculate state-of-charge. A new cell hasn't completed the charge-discharge cycle the BMS needs to calibrate its internal baseline, so the device reads the cell as lower than it actually is. This causes the low-battery alarm to fire even when the battery is at or near full charge. One complete charge-discharge cycle resets the BMS learning register and clears the false alarm.

Radical-7 won't power on after the replacement battery sat unused

Li-ion cells self-discharge during storage. If this battery sat long enough before installation, the resting voltage may have dropped below the Radical-7's BMS recovery threshold — typically around 2.5V per cell — which causes the device to appear completely dead. Connect the charger and leave it for at least 30–60 minutes before attempting to power on. If the charge indicator shows any activity, the BMS has accepted the cell and recovery is underway. If no indicator appears after 90 minutes on charge, verify the charger output is confirmed at 4.2V.