I was going to put a rechargeable 9 volt battery in my smoke alarm but someone was telling me that they read somewhere that a rechargeable battery should not be used in a smoke alarm, though they can't remember why this is.
Two reasons, both relating to the characteristics of NiCad (rechargeable) batteries:
- they discharge quite rapidly, even when under no load, so would need recharging quite frequently
- more importantly, they are prone to sudden loss of power at the end of their discharge cycle, so that there's no warning they've failed (most smoke alarms beep to let you know they need replacement batteries).
There are special long life batteries recommended for use in smoke alarms; they are designed for low drain and long life- your smoke detector may have a recommended model number indicated on the compartment. alternatively you could get a special lithium PP3 battery which should last for years but they're expensive. To be honest i wouldn't try and economise on something so simple yet important- a decent long life battery will probably cost about €6.
it shouldnt be a problem if you check the alarms regularly by pressing the test button. This is something you should do no matter what the battery.
My smoke alarms at home are actually wired into the house with rechargeable battery backup internally so I have the best of both worlds
I've tried them in the past and they don't really work very well. Normal non rechargeable batteries simply are not suitable for recharging. You may get some joy but you probably have more chance of the battery leaking or, worse still, exploding.
They exist alright, though they are more life extenders than anything, as they can't recharge a dead battery.You're also using something outside its design specification: I'd agree with Carpenter on not risking anything with a safety related device.Ideally, smoke detectors should be mains powered with battery backup (ideally rechargeable, trickle charged from the mains when it's on).For battery powered ones (far better than none at all), you should get at least a couple of years out of regular alkaline (e.g. Duracel) batteries: not a big expense, so why risk it?