Amazon.com: Tenergy Premium 9V Batteries Rechargeable High Drain 250mAh NiMH 9V Square Battery for Smoke Alarm/Detector, 20 Pack : Health & Household
Can I change the 9V backup battery safely in a smoke alarm without turning the main power off? - Quora
3PCS 9V 1200mAh Lithium Battery ER9V 9 Volt li ion Square Li SOCl2 Batteries for Toy Remote Control Microphone and Smoke Alarm|Primary & Dry Batteries| - AliExpress