Getronic GT904 7.2V Ni-MH Replacement Battery Alarm Siren

Getronic GT Auto Alarm Car Siren — 7.2V Ni-MH Replacement Battery (GT904)

This 7.2V, 80mAh Ni-MH battery replaces the backup power cell inside the Getronic GT Auto Alarm Car Siren, 944 Siren, and 945 Siren. It maintains siren function when the vehicle's main power is cut — the scenario this battery exists to handle. Dimensions are 45.70 x 30.80 x 7.50mm; confirm these against your existing cell before ordering.

• GT Auto Alarm, 944, and 945 compatibility: All three siren variants share the same internal battery bay, connector pin-out, and BMS handshake at 7.2V. The cell slots in without modification to the housing or wiring harness.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted the new cell without error flags, and the siren triggered cleanly on test activation without a mid-cycle cutout.
• Cover latch check after installation: Once the battery is swapped, close the siren housing fully and press the cover until you hear or feel the latch engage. Outdoor car sirens use a physical tamper switch tied to the cover — if it is not fully closed, many alarm panels will log a tamper fault and may misread it as a battery error.

Why the GT904 siren activates briefly then stops during an alarm event

An aged or recently installed Ni-MH cell at low state of charge cannot sustain the current draw the siren needs for a full activation cycle. When internal resistance is too high, voltage collapses under load and the siren's protection circuit cuts output. This is not a faulty siren — it is the BMS doing its job. After fitting a new cell, allow a full 24-hour charge on the alarm panel before running a test activation.

Siren battery depleting faster than expected between annual alarm tests

Ni-MH cells self-discharge at a higher rate than Li-ion, and outdoor temperature swings accelerate this. A siren mounted in an exposed engine bay or on an exterior panel will cycle through heat and cold, pushing the cell toward 0V faster than one in a controlled environment. A cell sitting at or below 6.0V will not reliably trigger the siren on demand. If your panel's battery health check fails within months of a swap, check the mounting location — relocating the siren to a less exposed position reduces thermal stress on the cell.