What's the life of...

Depends. If it's on a sunny wall, it'll last a little less time.

Thanks for that. It's at the top of the cellar stairs which have a door at the entrance, so no heat to speak of.

If you own a multimeter, and a suitable 12v(?) light bulb, it's fairly simple to test. Find a bulb that'll discharge the battery in 5 hours (Ah rating /5, so a

Yes - I could do that. But modern car batteries seem to just die overnight with no warning - I've had the most recent two do just this - so I was more interested in a rule of thumb for SLA type's life.

I fitted an alarm at both my brothers house and his next door neighbours over the same weekend. My brothers battery went down after about 2 years. The alarms PSU was buzzing loudly and changing the battery cured the fault. His next door neighbours is still fine after 5 years. I have a battery in my parents alarm that is over 7 years old and still works when I kill the power to do some work.

I think a car battery will fail anytime after the warranty and only on a morning when you must be somewhere important at a specific time.

Adam