CO monitor - replace battery?

[worms]

I have a CO monitor/alarm that is giving a low battery signal.  It is just under five years old, with a soldered-in-place battery.  Instructions say battery is not replaceable, but it would be really easy to just solder in a new one.  Unit has a guarantee of seven years but I have no proof of purchase and I have probably invalidated the warranty by opening it to look at the battery.

Should I replace the battery on the basis that the unit's electro-chemical detector should have a design life of at least seven years and still be ok? Battery cost is £4, replacement unit cost is £26.

[libertarian4321]

We ran into the same problem a couple of years ago.

Based on my research, it appears that these things have a very limited life span, often far less than what the package says.

We found that it was simpler to just replace the old unit. 

The good news is that the price on these units continues to drop.

[Greg]

Many detectors now have an end-of-life alert as well, intended to get you to replace them when they've reached their safe use limit.  If I had one that had a soldered-in battery that needed replacing, I'd replace the whole unit to prevent having a unit that didn't work even if the battery was good.

[Spork]

I've also had more than a little difficulty soldering to batteries.  It can be done, but you need a really hot iron and a lot of patience.  Batteries are a magnificent heat sink.  Most of the battery packs I see are done with a spot weld.