The exception is the 9v battery which actually has six smaller cells inside of it. [Tom] took a look inside three different batteries to see what cells they’re hiding. Since he no longer uses ...

Our evaluation included extensive discharge tests to find long-lasting alkaline batteries -- including AA, AAA, C, D and 9-volt options. We also considered the cost per battery for each option to ...

Generally, the best 9v battery for a smoke detector may last anywhere from 6 months to 2 years. Meanwhile, 9V lithium batteries typically have a longer lifespan and may last up to 5 years or more.