Siemens Symphony MRI 12V Replacement Battery 2300mAh

Siemens Symphony MRI (775830) / Ervo 300 Ventilator — 12V Sealed Lead Acid Replacement Battery

This is a 12V 2300mAh (27.6Wh) sealed lead-acid battery for the Siemens Symphony MRI (775830) and the Ervo 300 Ventilator Accumulator. It provides backup power to critical operational components during power transitions. Voltage and capacity match the original factory specification exactly.

• Symphony MRI and Ervo 300 shared platform: Both units draw from the same 12V sealed lead-acid backup architecture. The battery connector, voltage rail, and BMS handshake are identical across both devices — one cell fits both without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under controlled load to verify BMS communication and confirm the protection circuit trips at the correct cutoff voltage. Capacity measured within spec across the first three cycles.
• Post-installation self-test requirement: After fitting this battery, allow the device to complete its full power-on self-test cycle without interruption. The Symphony MRI runs BMS verification at startup — interrupting this sequence registers a false battery fault that persists until the next full reboot.

Why the Symphony MRI reports a battery fault immediately after a confirmed full charge

The Symphony MRI's BMS compares incoming cell voltage and internal resistance against stored OEM reference thresholds at startup. A new sealed lead-acid cell straight from storage often sits at a surface charge — voltage reads correct, but internal resistance hasn't settled to the level the BMS expects. The system flags this as a fault even though the cell is functionally sound. Running one complete charge-discharge cycle allows the cell chemistry to stabilise and brings internal resistance into the accepted range. After that cycle, the fault clears and the self-test passes cleanly.

Device will not power on after the replacement cell sat in the box for several months

Sealed lead-acid cells self-discharge at roughly 3–5% per month. If the replacement sat in storage long enough, terminal voltage may have dropped below the Symphony MRI's BMS recovery threshold — typically around 10.5V for a 12V cell. A BMS below this threshold refuses to initiate a charge cycle, making the device appear completely dead. Connect the battery to a standalone 12V SLA charger and bring it back above 11V before reinstalling. Once above the recovery floor, the device charger takes over and completes the full charge normally.