Audi A1 Emergency Supply Replacement Battery 7.4V 3G0915089

Audi A1 Emergency Backup Supply — 7.4V Li-ion Replacement Battery (3G0915089)

This 7.4V 2600mAh Li-ion battery replaces the emergency backup supply unit fitted across the Audi A1 range, including the 2025 Petrol Hatch 30 TFSI and 2019–2022 variants. It sits within the vehicle's emergency power module, keeping critical electrical functions active when the main 12V battery is depleted or disconnected. OEM part numbers 3G0915089 and 3G0915089A are the primary references; EC-VW-OCU3 and EAC63298904 are cross-references confirmed to the same physical form factor.

• A1 emergency module compatibility: The 2019 through 2025 A1 petrol variants share the same emergency power module housing, connector pinout, and BMS handshake protocol. The 3G0915089 cell pack slots directly into that module without re-pinning or firmware intervention.
• Bench tested on actual hardware: We cycled this pack through the module's charge and discharge sequence. The BMS accepted the cell within the first full charge cycle, passed the internal resistance check, and held cell voltage at 7.4V under the module's standby draw without triggering a fault code.
• Post-install charge cycle on the A1 module: After fitting, leave the vehicle on ACC or run a full ignition cycle so the module completes its charge sequence. The A1's emergency supply controller will not log a confirmed battery state until it has completed one full charge pass — skipping this step leaves the module reporting an uncertain runtime estimate.

Why the A1 emergency module logs a battery fault immediately after a fresh install

The A1's emergency supply controller runs an impedance check the moment a new cell is connected. A new Li-ion pack that has not been charged in the module will show a resting voltage slightly below the controller's acceptance threshold — not because the cell is faulty, but because it arrived in a partially discharged transport state. The controller interprets this as a failed cell and sets a fault. Placing the vehicle on a full charge cycle clears the impedance flag once the pack reaches 8.2V fully charged. If the fault persists after a full charge, check the connector contacts on the module housing for oxidation before assuming a defective cell.

Emergency supply showing full charge but not powering functions during a test disconnect

The module can display a full-charge indicator while the BMS has not yet completed its calibration cycle — the state-of-charge reading is estimated, not measured. After a battery swap, the controller needs one complete charge-to-discharge cycle before it trusts its own capacity map. Run the vehicle to full charge, then perform the manual self-test via the module's diagnostic routine in VCDS or the factory scan tool. A passing self-test confirms the BMS has accepted the cell at rated capacity; a failing test at this stage means the calibration cycle has not completed — allow two more hours on charge and retest.