So, be honest, who consistently checks for this defect on programmable thermostats, and if not, why not? (Note the expiration date).
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I did, ever since I found mine like that. 
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Pull the cover from a stat to see why its not working and run the risk of dealing with a homeowner asking why is my thermostat hanging there?
Nope.
Happens often especially when thermostats aren’t mounted well.
This may be a good area to stay within the SOP and simply note if the HVAC system works from controls.
The reason stated above is many of the thermostats are difficult to remove the cover, both programmable and non-programmable.
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Very good point, Scott!
Hope you and yours are well over there. I passed the big “C” and am still trying to get over the remnants of shingles…not enjoyable.
Thanks for your input.
FYI… in this instance, the thermostat worked perfectly. Like Larry, I learned long ago from past experience. I do however (lightly) attempt to remove, and if it doesn’t, gets mentioned as such.
I primarily posted this as I read all too often about inspectors getting called back due to systems not operating, and wondered how many could have been due to a battery condition issue. Do these same inspectors ever actually look at batteries? I have seen some where the corrosion is behind the battery and not easily seen without removal of the battery.
I’ve seen a few without good batteries. But my opinion is like Scott’s, this falls into the repair category and I’m not there to do repairs.
A similar find is a dirty flame sensor in a gas furnace. It would light, but not stay lit. After several unsuccessful attempts I wrote it up. The Realtor insisted it was something else. Go figure - they know everything!
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Being in Minnesota where Winters can get 50f below zero (plus wind chill factors) and Summers 110f degrees above ( and with 100% humidity)… it’s a risk I am willing to take! I would rather have to replace a thermostat than get that call the system doesn’t operate during extreme weather conditions!!
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I have come across some that already had dead batteries, and the vacant house/s have been very cold, with freezing conditions outside. I have batteries with me for times like this, have changed out batteries in this type of situation, and received thanks from realtors and/or home-owners. However, I don’t look inside all thermostats. A good reminder to add to a report is to remember to change thermostat batteries approximately once a year.
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If I can remove the cover without difficulty, I do. I also have discovered most of the batteries with corrosion on them are Duracell or Chinese brand.
You can always use a jumper at the furnace to turn it on - no batteries needed!
Whenever you go beyond the SOP, you should do so within your comfort zone and expertise zone. I know an HI who pulls furnace blowers so he can look up at the heat exchanger. The rest of us around here, genuflect in his general direction and leave the blower in the furnace.
So would I. I prefer to inspect the rest of the structure so it don’t fall on their heads and leave the furnace to the guy that is suppose to service it every year and put his name on the tag hanging on the furnace. LOL
Same…or, did. 
Back-up batteries do not run the thermostat,they just hold the program in the event of interruption of power…
Do you also climb up to every smoke detector and check those batteries?
It is a “defect”? No, it’s a potential future event which is not your job description.
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David, if the batteries go dead and there is no display, then the HVAC system does not operate.
I check the batteries for corrosion in the thermostat when I can. I also look at the date of the batteries.
In the winter, I do “snow bird” inspections for people going to Florida and leaving their homes vacant. For my clients, this is an important point of my limited “snow bird” inspection. (gets well below freezing in NE Ohio)
I do not list it as a defect but as a maintenance issue. Maybe not in the SOP, but I include it.
No, I do not check the batteries in the smoke detectors, but recommend in my reports to replace batteries every year and also replace the detector every 10 years.
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I only check stat battery dates if I have time - after checking the battery dates on the smoke alarms, CO alarms, garage door remotes, garage door backup batteries, sump pump battery, mini split remote, gas log remote, ceiling fan remote, home alarm controller, touch-less faucet, wireless doorbell, and Big Mouth Billy the singing bass - mounted over the fireplace.
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If there is no display (batteries or not) there is something wrong with the HVAC unit, not the batteries.
Batteries only hold the program in the event of a power outage.
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How about this Honeywell thermostat RTH1105?
"3.5 Battery Replacement Indicator
An icon appears when the batteries need replacement.
This icon will flash for 120 days, then the thermostat
will cut power to the heating/cooling unit. The icon disappears once the batteries are replaced. The temperature settings are saved and do not need to be re-entered.
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Or you can try a thermostat that connects directly to your system, without requiring batteries. Like this one https://popular.reviews/best-smart-thermostat/#3_Honeywell_RTH9580WF.
With the thermostats that I have replaced the batteries in, the batteries were required for the furnace/s to function, and the homes were very cold when I arrived at the inspections. Changed the batteries, and the furnace/s functioned. Some thermostats definitely need the batteries for the units to function.
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