Comment by jcgrillo

You make a good point about the furnace. It remains to be seen how long it'll last. My only hope is that it was designed to be serviceable.

I was very surprised to find the battery. This thermostat is designed to be compatible with older 3-wire systems, so I suspect they slapped a "10 year" battery in it and hope for the best. It's also marketed fairly deceptively. Or at least enough have fooled me--I thought I was buying an analog device.

EDIT: now I'm looking at the data sheets for an LM57 and getting some ideas