4 x Wilhelm Lithium 9V Block Batterie Rauchmelder 6LR61 9 Volt Batterien : Amazon.de: Baumarkt
GP Lithium 9 V Block Batteries, 9 Volt Lithium Li-MnO2, 10 Year Battery Longlife Ideal e.g. as a Smoke Alarm Battery, for Fire Detectors, Microphones etc.: Amazon.de: Electronics & Photo