Energizer Ultimate Lithium 9V Batteries (4-Pack, L522) - Long-Lasting Power for Smoke Detectors, Toys & Electronics

Didn't seem to fit in my smoke detector. Discovered the battery has such square corners, it was catching on the detector's plastic tab that doesn't allow you to close the battery tray without a battery installed. Normal batteries are slightly rounded so they will push the tab down rather than catch on it. Fortunately there is room to help the tab retract on the back side of the open drawer so you can fully insert the lithium battery thereby depressing the plastic tab fully so the battery fits and the tray closes. I'm looking forward to many years with no beeping from weak batteries. Didn't rate longevity or battery life as these are newly installed.