Honeywell RTH6400 - Manual (Page 20)

Operating Manual
69-22ES—0 8
About your new thermostat
M28414
M28413
Replace Battery
Battery replacement
Install fresh batteries immediately when the
REPLACE BATTERY warning begins flashing. The
warning flashes about two months before the
batteries are depleted.
Even if the warning does not appear, you
should replace batteries once a year, or before
leaving home for more than a month.
If batteries are inserted within two minutes, the
time and day will not have to be reset. All other
settings are permanently stored in memory and
do not require battery power.
Press down and pull to remove.
Insert fresh AA alkaline
batteries, then reinstall
battery holder.