Owner's Manual
Page 21
Even if the warning does not appear, you should replace batteries once a year, or before batteries are optional (to provide backup power) if your thermostat was wired to remove from wallplate M28103 Batteries are depleted. Install fresh batteries immediately when the LO BATT warning begins flashing. Battery replacement RTH7400/RTH7500 Series Grasp thermostat and pull to run on AC power when installed. The warning flashes about 30 days before leaving home for more than a month. Insert 2 fresh AA alkaline batteries M28101 19 69-2222EF-03
Even if the warning does not appear, you should replace batteries once a year, or before batteries are optional (to provide backup power) if your thermostat was wired to remove from wallplate M28103 Batteries are depleted. Install fresh batteries immediately when the LO BATT warning begins flashing. Battery replacement RTH7400/RTH7500 Series Grasp thermostat and pull to run on AC power when installed. The warning flashes about 30 days before leaving home for more than a month. Insert 2 fresh AA alkaline batteries M28101 19 69-2222EF-03