Smoke alarms! That's another thing! The ones here are mains powered but with PP3 battery backup. And of course they both ran out in the middle of the night and started bleeping
I don't see why the battery gets used at all if it's mains powered, I would have thought the battery should only get used if the mains goes off, but it seems like the battery is running down all the time.
That going bleep in the middle of the night is indeed most annoying. And due to the air temperature being lower at night, that's also the most likely time that they will decide that the battery is low.In my experience rechargeable 9V have very poor lasting power. Also, the ordinary rechargables have a significant self-discharge rate, which won't be helping. I'd very probably put an ordinary 9V into a smoke alarm.
It's for this reason that I use Lithium (non-rechargeable) 9V PP3 batteries in them. Plus it saves the effort of having to get the step ladder out so often to change them. The Lithium (non-rechargeable) 9V PP3 batteries last around ten years.
All cells and batteries will self discharge if left long enough even if not connected to anything else. Lithium (non-rechargeable) have a very long shelf life of greater than ten years. Alkaline are half that at best. When used in a typical smoke alarm, they typically last between one and two years.
For mains powered smoke alarms with battery back-up, the battery should last longer than battery only smoke alarms. But due to self discharge and a very small amount of current used by the smoke alarm to check the charge status, they will eventually trigger the low battery alarm.
I don't recommend using rechargeable batteries in smoke alarms.
This is what I am currently buying for use in smoke alarms:That one came from Rapid (as I was placing an order anyway for something else) but CPC and Farnell also stock them I think. The Rapid order code is 18-3942.
Mark
Statistics: Posted by 1024MAK — Fri Dec 06, 2024 3:09 pm