Our 15-year old external alarm box is still electrically OK but looks
very shabby. So I'm either going to have to attempt to clean and
repaint it or replace it with an entire new unit.

Researching the latter option, I see that many current products
have a built-in battery, typically NiMH rechargeable. But my main
alarm unit downstairs (15 years old) already has a 12V standby battery
(lead acid). Isn't that true of most such units? If so why is another
battery needed in the bellbox itself please? And why are they
apparently 7.2V or 8V, not 12V?

Also, are these batteries truly maintenance-free (not my experience of
many NiMH batteries)? Installing the bellbox under the eaves will be
hazardous enough, but I don't relish having to get up there again
regularly to attend to the battery.

--
Terry, East Grinstead, UK

Lead-acid batteries are commonly used in such applications. My alarm system
uses one as a backup in case the AC fails.

There is no such thing as a "maintenance-free" battery, because it will
eventually fail and need replacement.

Once upon a time, lead-acid batteries were not sealed, and required period
addition of water. This is no longer true.

In article ,
William Sommerwerck wrote:
Lead-acid batteries are commonly used in such applications. My alarm
system uses one as a backup in case the AC fails.

They're common in the panel - but all the ones I've seen inside the
external sounder or 'bell box' are Ni-Cad or similar. But purely to make
it more compact, I'd guess.

--
*"I am " is reportedly the shortest sentence in the English language. *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
William Sommerwerck wrote:
Lead-acid batteries are commonly used in such applications. My alarm
system uses one as a backup in case the AC fails.

They're common in the panel - but all the ones I've seen inside the
external sounder or 'bell box' are Ni-Cad or similar. But purely to make
it more compact, I'd guess.


A lot of modern bell boxes contain a battery which energises the
bell/siren in the case of attack i.e. cutting the wire to the box. This
is in addition to the back up battery in the alarm panel.

Ron(UK)

In article ,
Ron wrote:
Dave Plowman (News) wrote:
In article ,
William Sommerwerck wrote:
Lead-acid batteries are commonly used in such applications. My alarm
system uses one as a backup in case the AC fails.

They're common in the panel - but all the ones I've seen inside the
external sounder or 'bell box' are Ni-Cad or similar. But purely to
make it more compact, I'd guess.


A lot of modern bell boxes contain a battery which energises the
bell/siren in the case of attack i.e. cutting the wire to the box. This
is in addition to the back up battery in the alarm panel.

Not just modern - this has been the case for many a year. More or less
from when alarms became common on domestic premises.

--
*What was the best thing before sliced bread? *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Ron wrote:
Dave Plowman (News) wrote:
In article ,
William Sommerwerck wrote:
Lead-acid batteries are commonly used in such applications. My alarm
system uses one as a backup in case the AC fails.
They're common in the panel - but all the ones I've seen inside the
external sounder or 'bell box' are Ni-Cad or similar. But purely to
make it more compact, I'd guess.


A lot of modern bell boxes contain a battery which energises the
bell/siren in the case of attack i.e. cutting the wire to the box. This
is in addition to the back up battery in the alarm panel.

Not just modern - this has been the case for many a year. More or less
from when alarms became common on domestic premises.

well... I meant modern for me!