Often the battery operated smoke detectors take 9V batteries.
I want to replace batteries less often. Question Why do smoke detectors run off 9v batteries? doesn't offer a clue.
Should I look for capacity, and at which current draw?
Or should I look for another specification to choose a replacement battery for a smoke detector?
A battery operated ionisation smoke alarm typically draws less than 0.1 mW.
The background power requirement for photoelectric smoke alarms is similar to ionisation smoke alarms (typically around 0.2 mW).
With a current draw of typically 10 μA to 20 μA, the life of a 9V cell with a capacity of several hundred mAh will probably be limited by the battery shelf life rather than the energy capacity of the battery.
source: https://www.energyrating.gov.au/sites/default/files/documents/sb200405-smokealarms_0.pdf#page9
Use a mains-powered smoke detector so it won’t draw any current from the battery, besides diode leakage (typically).
Use a long life lithium 9V battery.
This combination will easily last the life of the smoke detector - 10 years. Since consumer smoke detectors have to be replaced every 10 years, you’ve got 0 battery replacements and you can’t do any better than that :)
If the alarm is activated rarely, then you can just buy “10 year” detectors that have a built-in primary lithium cell rated to last at least 10 years. No mains power needed. Then you won’t even have to buy the battery separately.
If your smoke detector is over 10 years old, you have to replace it!
