I have a Luxpro thermostat, and in the battery compartment it has warning saying to use only Energizer or Duracell AA batteries.
Is there a technical reason for this? Or is this BS?
My guess would be that perhaps they want you to use longer-life alkaline batteries instead of some cheapo Ray-O-Vacs that aren’t going to last as long. I’m not sure why they couldn’t specify “alkaline batteries” though instead of specific brand names.
I would have said they have an endorsement deal with the battery company, but seems less likely if they recommend the two biggest competitors in the business.
Possibly they want you to avoid using cheap batteries that might leak and ruin the unit.
This would be my guess.
They probably get tons of bad 'stats back that were damaged by leaking no-name batteries. By specifying a better quality battery, they can cut down on returns.
they are quality long lived batteries. if you used lower quality batteries, like a store brand, they might need to be replaced more frequently. if you needed to replace batteries frequently then you might develop a dislike for that seeming ‘battery eating’ thermostat and tell all the people you know to stay away from that brand.
There is no technical reason, except to try to ensure that the battery life is consistent.
Physically and electrically, an alkaline AA cell is an alkaline AA cell, regardless of manufacturer, even if some have lower overall capacity then others.
ETA - I don’t know what your thermostat is, but my electronic/programmable one for the heat pump only uses the battery to keep the program intact, and the clock running if the power goes off. There is a slight chance that they recommend the ‘Big Brand’ batteries because they are less likely to leak then off-brand ones are, but that is only conjecture, and meaningless if you change them out every year or two.
This is so not true.
Different manufactures use different techniques when they make their batteries. Cheap batteries have much poorer seals and thinner case metal. They leak more often than better quality batteries.
Change your battery once a year, say at the beginning of heating season.
One time my cheap battery failed while the heat was ON, so it just kept running. I woke up at midnight, and the house was about 95 degrees!
That was unrelated to the batteries…
I would tend to agree with CookingWithGas.
I suspect any alkaline battery will work, although I only use Duracell.
Not mentioned yet is the difference between alkaline and rechargeable batteries. One thing I’ve noticed with my thermostat is that when I use NiMH instead of alkaline, the LCD is considerably dimmer. That is unique to thermostats, in my experience – every other LCD-bearing device I’ve used NiMH is just as bright & legible as it would be with alkalines.
a NiMH battery at fulll charge is 1.2V
an alkaline battery at full charge is 1.5V
i have some devices that don’t run long at 1.2V (or just below). depends on how the device was engineered.
I have seem minor, but significant differences in physical dimensions between brands.
I used to have an SLR that used a lithium battery, and it was a known issue that Name Brands W and X simply would not work reliably unless you cut a shim out of a business card so the contacts would be secure.
Where you there? What was it, then?
Rayovac claims their alkalines last just as long.
I’d put te blame on Mrs. Frisby and the Rats 
Yeah, I guess that wasn’t very clear. I didn’t mean the Rayovac alkalines, just their cheaper “heavy duty” batteries. In fact I have a package of them here in my desk and it says “For higher drain devices use Rayovac alkaline”.
Batteries-----weak or strong couldn’t have caused it.
It could have been the thermostat, but not the batteries in the thermostat.
As Khendrask pointed out, the batteries just hold the program. They don’t have anything to do with the actual operation of the furnace.
Hmmm, that’s weird then. I wonder what it was? Even the furnace guy said it was the battery.
Oh well, hasn’t happened since.
Don’t programmable electronic thermostats need power to keep the internal thermometer and electronics going as well? If I pull the batteries, the thermostat will stop determining current temperature and comparing it to programmed temperature, and thereby signalling the furnace, won’t it? I can see a badly designed one leaving the connection that tells the furnace to turn on connected when the batteries get weak.