Philips HeartStart FRx 9V Replacement Battery M5070A

Philips HeartStart FRx / OnSite / HS1 — 9V Li-MnO2 Replacement Battery (M5070A)

This is a 9V lithium-manganese dioxide battery rated at 4200mAh (37.8Wh), replacing OEM part M5070A. It fits the Philips HeartStart FRx, OnSite, HS1, and Home Defibrillator AED platforms. Compatibility also covers OEM cross-references M5066A, M5067A, M5068A, 861304, and 110300.

• HeartStart AED platform fit: The FRx, OnSite, HS1, and Home Defibrillator all share the same battery bay format, connector pinout, and BMS handshake protocol — that is why one cell covers the full range. The 9V rail is fixed; any deviation trips a hard fault before the device reaches ready state.
• Bench tested on actual hardware: We ran this cell through the HeartStart FRx startup sequence and confirmed the BMS handshake completed without fault. The device reached ready state and the charge indicator cleared. No false low-battery flags appeared after the self-test cycle finished.
• Post-installation self-test protocol: After fitting this battery, let the AED complete its full power-on self-test without removing or reseating the cell. The HeartStart platform runs a BMS verification pass at startup — interrupting it mid-cycle logs a battery fault that persists until the next clean reboot.

Why the HeartStart FRx shows a battery fault on a freshly installed cell

The FRx BMS compares internal resistance and open-circuit voltage against a stored OEM chemistry profile on every boot. A new Li-MnO2 cell that has not yet completed one full charge-discharge cycle sits outside that window and triggers a fault flag. This is not a cell defect — it is the BMS applying a conservative threshold before it trusts an unvalidated cell. Run one complete self-test cycle with the battery seated and undisturbed. The fault clears once the BMS logs a passing verification against the 9V rail.

AED not powering on after the battery sat in storage

Li-MnO2 chemistry self-discharges slowly but continuously during storage. If the cell voltage drops below the BMS recovery threshold — typically around 6V for this platform — the device will not initialise, even though the cell still holds significant capacity. The BMS locks out to protect the AED's charge circuitry from an undervoltage condition. Measure the battery's open-circuit voltage with a multimeter; if it reads above 7.5V, reseat the cell firmly and allow a full 60-second boot. If it reads below 7V, the cell requires replacement before the device can be returned to service.