burglar alarm battery

5 Apr 2004
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United Kingdom
I recently turned off the mains in my house, and immediately the burglar alarm outside started making a weak "strangled duck" type noise. I restored the power and the alarm went off in tamper mode.

I have cut the power many times in the 2 years I have been in this house, and the alarm has never done this before, so I would suspect a dead backup battery inside.

I've opened it up and it's a DETA 12V rechargable sealed lead-acid battery.

A couple of questions...

1) should the battery recharge itself when the mains is connected? If so, the fact that 2 weeks later the tamper is still happening as soon as power is cut means this recharge musn't be happening.

2) If it doesn't recharge, how do I go about recharging it, will a car battery charger do the trick?

Any help appreciated.
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Have you tested the battery?

If it is a 2+ year old lead-acid type, that's gone flat, then it might be sh*gged....
you must not charge a sla with a car charger it can damage them

wither the battery is dead or the charge system is but it's difficult to tell which withotu having a suitable charger
well I've just discovered that replacement batteries are under a tenner, so problem solved.
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for what its worth, the batteries are "trickle charged" and should be changed every 5 years
I did find that SLA can occasionally get into a state whereby they do not back-up the alarm panel - a meter across the terminals with a load shows a low reading.

I managed to "shock" the battery back to life (less than 5 years old) by connecting a 5W car bulb across it. It took a few attempts to get it to work but it has been fine since. Probably something to do with the chemistry but I haven't looked any further

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