Do Thermostats Need Batteries?

Most of them do, but If you're looking for a battery-less thermostat, then we've put together this list of the best-selling battery-less thermostats for you:

Many homeowners don’t recall changing the batteries on their thermostats. In many cases, many don’t even know that these devices have batteries in the first place. When the air-conditioning unit or the furnace suddenly fail for no apparent reason, then they discover that, indeed, thermostats need batteries.

Energy Storage: Do Thermostats Need Batteries?

While many programmable thermostats run on a 24-volt common wire (i.e., C-wire), manufacturers recommend placing batteries in these heating and cooling control units. The batteries are useful in retaining the thermostat’s temperature and time settings after a power outage, which may not happen often but can happen at some point.

These then act as a source of the uninterruptible power supply (UPS) for the thermostat – and we all know its importance if you have ever used a desktop computer with a UPS device.

You can obviously reset the thermostat’s previous settings after these have been erased due to a power outage. But you have to spend time and effort on the task, which could be better spent on other things.

This is especially true when you already have weekday and weekend schedules programmed, which will require you remembering all the energy-efficient settings – and you may not be able to do so. You will then find yourself starting from square one, no thanks to your failure to place batteries on your thermostat or to your ignorance of annual battery maintenance.

When a thermostat doesn’t have good batteries in it, the readings can be inaccurate, especially in battery-operated units. The inaccuracies will have a negative effect on the temperature and time settings, resulting in inefficient energy use. This would defeat the primary purpose of a digital programmable thermostat.

The bottom line: Yes, thermostats need batteries unless, of course, the thermostat in your home is only powered by the main grid. But if your home’s thermostat has a battery compartment, you should place batteries in it.

What Are the Signs to Look For?

Most of the thermostats installed in homes today are the digital type. It’s a safe assumption to make since mercury thermostats seem to be on the way out because of their extremely basic manual functions.

Most of the digital programmable thermostats are operated in one of three ways, namely: by batteries alone; by plugging into an electrical outlet; or by both battery and electricity.

The third type is the most common for obvious reasons, especially for homeowners who don’t want to go to the trouble of reprogramming their thermostats. For this reason, these products are usually designed with low battery alerts including the following:

  • The touchscreen display has gone blank.
  • The HVAC system and/or thermostat cannot be turned off or programmed.
  • The LED screen displays odd characters that shouldn’t be there in the first place.
  • The battery icon displays an alert status, such as a red empty battery flashing on and off.
  • The air-conditioning unit or furnace isn’t operating as reliably as before.

In case you have a smart thermostat with a companion app downloaded to your smartphone, tablet or laptop, you may even receive email alerts about replacing the batteries, as is the case for air filter replacements. You should always check if the batteries require changing since you don’t want to do it after these have been completely drained of their juices.

You should also check the instruction manual about the regular battery replacement schedule. You may have to change the battery on an as-needed basis or once a year depending on the model.

What Are the Steps to Change Batteries?

Be sure to read your thermostat’s instruction manual first before changing the batteries for the first time. The following steps are general in nature, so there’s no substitute for following the manufacturer’s step-by-step instructions on this matter.

You should gather your tools first, which may include a small flat-blade screwdriver. You must also have the right type of batteries on hand and ready for replacement. You must, again, consult the users’ manual for more information about the battery type, which can be AA or AAA alkaline batteries, perhaps even lithium batteries.

Tip: Never install damaged batteries, such as those with leaks or dents, since these can also damage the thermostat’s electronic components. These can result in inaccurate displays of temperature settings that, in turn, will likely increase your energy bill. Keep in mind that even a single degree lower or higher than the recommended setting can result in a significant increase in energy consumption.

  • Pull the thermostat’s housing off its mounting plate.
  • Turn it over so that the battery slots can be seen.
  • Remove the old batteries with a screwdriver.
  • Place the new batteries into the slots.
  • Replace the cover and mount the thermostat on the wall again.

The battery replacement process is simple so there’s no need to call a professional electrician. You may not even have to turn off the thermostat, but it depends on the model.


Batteries on thermostats are important for their proper functioning. We suggest checking their integrity (i.e., good condition) and then replacing them when needed.

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