Ten months later, and I still have not mounted the 5-in-1 sensor at its final location!
(The humidity sensor has been having some accuracy issues, and I've been too busy to do the warranty thing.)
To AcuRite's credit, the Duracells that I installed last December are still going strong. I was figuring 3-6 months out of a set, but these may make it a full year if the cold weather doesn't get them.
From what I read in another thread either here or on AcuRite's web site, the 5-in-1 sensor is just like the indoor consoles where it uses two "banks" of batteries and not all of them in series. This allows battery changes without losing your data, provided that you only take out one "bank" at a time. Long story short, I have not taken a multimeter to the 5-in-1 yet to verify this, but suspect that it only needs 3 volts (two D-cells) to run it.....