9-volt smoke alarm batteries come in 3 types, ranked by increasing energy storage and price:
- the original carbon-zinc (often labelled “heavy duty”)
- alkaline (which hold more energy and so last longer)
- lithium (which hold even more energy and can last in a smoke alarm for many years).
Our testing shows a good alkaline battery has about twice the life of a carbon-zinc battery – and a good lithium battery has 3 times the carbon-zinc’s life.
The “cold performance” score in our test looks at how well a cold and half-discharged battery could power a sounding smoke alarm. The good news is that all types of smoke-alarm batteries were capable of sounding an alarm when cold and half-discharged.