Owner's Manual
Page 11
... flashes about two months before leaving home for backup power) if your thermostat was wired to the display during power interruptions. Install fresh batteries when the REPLACE BATT warning begins flashing. Turn thermostat over, insert fresh AA alkaline batteries, then reinstall thermostat. Replace batteries once a year, or before the batteries are permanently stored in...
... flashes about two months before leaving home for backup power) if your thermostat was wired to the display during power interruptions. Install fresh batteries when the REPLACE BATT warning begins flashing. Turn thermostat over, insert fresh AA alkaline batteries, then reinstall thermostat. Replace batteries once a year, or before the batteries are permanently stored in...