It’s December and the temperature is falling. The fireplace is roaring, the heaters are blowing, and hopefully the trustworthy smoke detector is vigilantly monitoring the whole house. I am sure that this Fall everyone checked the batteries in their smoke detectors and replaced them as needed. But, what kind of battery did you use in the smoke detector?
Hopefully, you did not use rechargeable batteries in you smoke detector, or if you did you used a low self discharge rechargeable battery. Here is why…
Common NiMH and NiCd rechargeable batteries have a high self-discharge rate, making them unsuitable for use in smoke detectors. This is true even though they may provide much more power than alkaline batteries if used soon after charging, such as in a portable stereo. Also, a problem with rechargeable batteries is a rapid voltage drop at the end of their useful charge. This is of concern in devices such as smoke detectors, since the battery may transition from “charged” to “dead” so quickly that the low-battery warning period from the detector is either so brief as to go unnoticed, or may not occur at all.
There are few winners in the rechargeable battery world that you might think as perfect for you smoke detector. Normally, these long lasting rechargeable batteries are constructed with Lithium-ion. However, the down side is that they have a very high discharge rate which can run as high as 12% per month, and the final decay rate is unstable.
Normally, you would just go out and buy a disposable lithium (not lithium-ion) and just toss it each year as a matter of security. However, now there is a variety of rechargeable batteries that are better suited for the slow power requirements of smoke detectors: Hybrid rechargeable… these batteries can save you hundreds of dollars in the long run, and they’re better for the environment than disposable batteries. The best brands come pre-charged and hold their charge for years, so they’re just as convenient as disposables.
I researched the options for these hybrid rechargeable 9 volt batteries and here is a good choice: Premium AccuEvolution 9v NiMH Precharged Low Self Discharge Rechargeable Batteries. AccuEvolution has an extremely low self discharge rate (less than 2% per month at room temp), so it stays charged for quite a while — which is absolutely essential for smoke alarms