Honeywell th1100d1001 thermostat keeps flashing low battery light stops working. Changed batteries multiple time. Works for a day or so. Cools fine but not sure if more serious issue.Single female.

Get the common hooked up on both indoor unit and tstat and be done with batteries all together!!!

Sounds like a glitche in the thermostat. First, override the program & see if it does the same thing over the next few days.

I have ran into this problem before. I have actually had low batteries I thought were good too ha! I have had to actually reset the stat to get the low battery to stop flashing. There are multiple ways to reset the thermostats, depending on model, but removing the batteries and waiting has worked, along with actually having a reset button somewhere on the stat. Hope this helps!

The low battery light will stop flashing when the new battery you just installed become fully charged. It will take some time for the new battery to become fully charged.

Try to find a reset button or just change out the thermostat. I'm guessing you don't have the manual. Thats a pretty old model, I think you have to set the time and day before you can use the thermostat.

If you have a spare wire (unused) in the thermostat wire sheath you can eliminate the batteries as the power source.
Turn off the power to the furnace.
Open the thermostat and look for terminal "C". If it is not being used,then
look inside the furnace for the thermostat wire terminals. Black or blue are probably not being used. Take one of these wires and strip insulation back 1/2 inch. Connect this wire to the COMMON (C)(-)wires from the low voltage transformer.
Open the thermostat and connect the same wire to the "C" terminal on the thermostat.

You need to change batteries. The bat lo light flashes when you have about 10% battery life left. Rus

Sounds to me like you have a low voltage short. If the stat had no display until you installed the battery means there was no voltage for the stat to work. Putting the battery in proves the stat works, no motors turning on probably leads to a blown low voltage fuse generally a blade fuse on circuit board in indoor unit. Good Luck

I had this same problem today.  I called Honeywell and they said the flashing broken battery symbol may mean low batteries, or it may mean the battery type is incorrect.  They recommend only non-rechargeable alkaline batteries.  I was using rechargeable NiMH batteries.  Even though they were fully charged, I had the flashing battery symbol and the thermostat relay would not work.  I replaced with alkaline, the flashing battery indicator went out, the thermostat works again.
Odd that it worked for 3 months on the rechargeables after first install. I did notice the broken battery symbol came on after the first few days, but I checked the battery charges and they were good, so I disregarded the symbol until the thermostat stopped working today.  Apparently there is something about the NiMH performance characteristic that the thermostat doesn't like.