🚀 go-pugleaf

In article <867o75$i3q$1@nnrp1.deja.com>,
  Bhoot Nath <bhoot@my-deja.com> wrote:
>Three of the six smoke alarms in began chirping a few days back. I
>presume that this means that the 9 volts batteries must be replaced.
>
>So, we thought, rather than buying alkaline batteries, why not buy
>rechargeable ones. We already have a recharger that works with
>AA/AAA/9V etc.

It's dangerous to charge alkalines in a charger designed for nicad or
NiMH batteries becuase the pressure can build up to well over 50 PSI
internally and cause rupture.  Also, alkalines just don't recharge well
unless they're designed for that purpose (like Renewals), but even
those are good for only 10-20 recharges.

>1. Should we get Nickel Cadmium (NiCad) or Nickel Metal Hydride (NiMH)
>batteries for a smoke alarm? Is there a reason to prefer one vs other?

>2. We looked at an EVEREADY pack and it was marked "9 volts (Use 7.2
>volts)" ... Does this mean it would deliver only 7.2 volts? If so, is
>it safe to use it for a smoke alarm? If not, are there any rechargeable
>9 volt batteries that deliver 9 volts?

UL approved smoke alarms are required to contain circuitry to warn when
the battery is low and to continue operating normally for at least 30
more days.  This circuitry measures the voltage, and nicad and NiMH
batteries in this size are too low in voltage even when fully charged,
either 7.2V or 8.4V.  And unlike alkaline and lithium batteries, nicad
and NiMH batteries put out a nearly constant voltage until the end,
meaning the low-battery warning may not be noticed because the battery
will go completely dead so quickly.

>3. On a web site, I also saw a reference to "Super long lasting,
>industrial strength 9 volt alkaline batter"  for $20, about 10 times
>what a regular 9 volt battery costs. Any one has any experience with
>this kind of battery? WOuld it last 10 years in a smoke alarm?

Duracell makes some high-capacity alkalines with about 70% more energy
capacity than normal alkalines, but they don't last any longer in
storage.  Because smoke detectors draw very little power, their
batteries are more likely to run down from normal spoilage than
anything else, in about 2-3 years.  But there are lithium batteries
with not only 3 times the energy capacity but also 3 times the shelf
life, and they will last 10 years in a smoke detector.  In fact some
detectors with them are guaranteed for 10 years.  Kodak Ultralife is
one brand of lithium 9V battery, and it's also sold under the brand
name of one smoke detector.


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