I want my house to be more proofed for things like temporary power outages,
etc, in case we are not around.

Do what everyone else does with these thermostats - put in new batteries when
Daylight Saving time rolls around. Why get all worked up about something that
is your own responsibility? You can get control systems that are fail-safe and
fool proof, but unless you have a seven figure income they may be priced beyond
your budget. Odds are your batteries had gone way beyond their stated effective
life, so if you tend to be forgetful, get the highest quality replacements on
the market.
Maybe a warning tag on your furnace filter compartment would be helpful for
next year. HTH

Joe