They’re not so expensive
Although I will say that I’m completely unable to tell you how long their batteries normally last. I have two of those exact SmartThings Multisensors, but I’ve converted both to be triggered by contacts closing and both are converted to run off a 5v power adapter. But, they do not drop off the network and one of them is in my basement, shrouded by a lot of unavoidable metal.
You’ll see in the post I linked to above, that one of the reasons I converted both to mains power was that I experienced a dead battery 24 hours after my hack. I’m sure my connection of relay dry contacts to the hall sensor caused this, because that would obviously never fly as an off-the-shelf product if the battery died that fast. I’ve not seen others here complaining about their battery life, so you shouldn’t have any trouble either.
