I got just over six months of life before having to replace the batteries.  It's possible I'll get more with a fresh set because the original ones were mixed (different brands) and when I checked them at removal one was open - so maybe a weak cell to start.

One mechanical problem:  the battery clips are junk.  They aren't spring steel and I found that over time the clips would relax and the unit would stop working.  Also if it gets dropped the battery mass is enough to bend the clip contacts.  I had to open the case a few times thru the 6-month period to correct this.  If I build more I'll switch to a higher quality clip.

Other than that it works great and, comparing to my phone's weather widget, it's been accurate to +/- 1C.