Audi A1 Emergency Supply Compatible Battery 7.4V 3400mAh

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

This is a 7.4V, 3400mAh Li-ion replacement battery for the emergency supply unit fitted to the Audi A1 and closely related Volkswagen Group platforms. It powers the vehicle's emergency lighting and eCall communication systems when the main 12V supply is lost. Compatible across the A1 2019, 2022 Petrol Hatch 35 TFSI, 40 TFSI, and 2025 30 TFSI, plus 26 additional fit models sharing the same OEM part number 3G0915089.

• Multi-model compatibility across VW Group platforms: These models share a common emergency supply module with the same connector pinout, BMS handshake protocol, and 7.4V cell configuration — that's why one replacement battery covers such a wide range of vehicles.
• Bench tested on actual hardware: We ran this battery through the emergency supply module's charge and authentication sequence. The BMS accepted the cell ID, completed the charge cycle, and the unit cleared its fault register without manual reset.
• Post-install charge cycle requirement: After fitting, leave the vehicle connected to mains via an OBD charger or run the engine for an extended period — the emergency supply module will not flag the battery as ready until it has completed one full supervised charge cycle through its own controller.

Why the emergency supply unit shows a fault immediately after battery swap

The A1's emergency supply module runs a battery authentication check the moment a new cell is connected. Until the module completes a full charge cycle and records a valid end-of-charge voltage — typically 8.4V for a 7.4V Li-ion pack — it holds a fault flag in the system log. This is not a faulty battery. It is the module's calibration sequence protecting the eCall function from an uncalibrated runtime estimate. Allow the module to complete a full charge without interruption and the fault will clear itself.

Emergency system not powering eCall or lighting during a simulated outage

If the module draws from the replacement battery but devices still don't activate during an outage test, the battery has not yet been accepted by the module's management firmware. The module holds output disabled until it has logged at least one complete charge-to-discharge cycle and confirmed the cell can hold above 6.8V under load. Trigger the module's self-test through the vehicle diagnostic menu after a full charge. If the self-test passes and voltage under load reads above 7.0V, the system is functional.