Tenergy 6LR61 9V Alkaline Battery, Non-Rechargeable Battery for Smoke Alarms, Guitar Pickups, Microphones and More, 240 Pack

Customers find these batteries work well for smoke detectors and are as good as name-brand alternatives. However, the battery life receives mixed feedback - while some report they last 10 years, others say they only last 4 years. Moreover, customers report issues with size, noting they are larger than standard, and with reliability, as some units fail within a year. The voltage performance is also mixed, with one customer reporting units with voltages ranging from 2V to 8V.