Does low battery affect a thermostat?

Wall thermostats use AA or AAA alkaline batteries, but you will also find many more using 3V button-style lithium batteries. Batteries are essential for your thermostat to remember its programmed settings. You won’t have to reset your thermostat after a power outage.

Most thermostats will display a low battery warning approximately two months before the batteries die off completely. But what does it mean when your thermostat says low battery and you don’t replace it? Does a low battery affect the functionality of the thermostat?

A low battery can affect your thermostat in different ways. First, it will prevent the cooling and heating system in your home from running effectively. In the event of a power outage, you may lose all the programming or energy-saving settings. Lastly, you risk your thermostat display going blank when the battery is low, meaning that you will be unable to control your HVAC system.

What happens if a thermostat battery dies?

It is not a good idea to leave the batteries in your thermostat to die completely. The consistent and effective operation of your HVAC system depends on it.

When the battery dies:

The thermostat display goes blank

When the thermostat battery dies, its display will go blank. That means you will be unable to control it. You will also lose your data, including the energy-saving settings.

The HVAC system will not work

When batteries die, the unit will no longer operate the HVAC system. The risk is that it might lead to excessive cooling or heating of your home. Or, your home will not heat or cool.

The thermostat won’t respond to commands

Your thermostat will not respond to your commands when the battery dies. If your device answers to voice commands, telling it to raise or lower the temperature or turn on the heating or cooling will not work.

Odd thermostat behavior

You will see some odd behavior if there is insufficient power to operate a thermostat. The unit will be inconsistent in its operation. For example, your system will not turn on, turn off and on repeatedly, or make strange noises.

How long do thermostat batteries last?

Batteries in a thermostat can last from eight months to up to a year. However, that will depend on the type of thermostat you are using. Some can last up to two years.

Once this period elapses, you will need to charge it, if necessary. If the battery is not chargeable, you will have to replace it with brand-new high-quality batteries.

How do I know if my thermostat needs a new battery?

Depending on your thermostat, you will see a warning at least two months before the batteries die. The sign may come in the form of words indicating a low battery or a flashing light.

At this time, you should replace the batteries with new ones. Also, if the battery keeps draining fast, consider replacing it with a new one. When getting replacement batteries, go for those with a higher or the recommended voltage.

But in some cases, the thermostat may not give you a warning about low battery. Instead, it will start behaving oddly. For example, you will notice the thermostat beeping unremittingly. In other cases, your HVAC system stops operating as it should. In some cases, the display will go blank and prevent you from setting it or turning it on.

Whenever you get any of these issues, check the battery first and replace it if necessary. Many manufacturers also recommend that you buy a new battery after using the old one for a year.

I changed batteries in a thermostat and now nothing works

If you changed the batteries in your thermostat and nothing works, try to troubleshoot the issue using the steps below:

  • Check to ensure all the wires are secure behind the thermostat.
  • Take off the panel on the AC unit, and push in the door trigger to determine if the lights are working. If the lights are working, there is enough power going to the whole system but not reaching the thermostat.
  • Check the fuse on the primary circuit board that has the number “3” on it. Ensure you have not blown it. Otherwise, you will need to replace it.
  • Check the AC condensation overflow pipe to determine whether it has a clog. If there is a clog, the safety valve will cut off the power and prevent it from reaching the thermostat. Therefore, you need to unclog it and turn on the thermostat.

If all troubleshooting steps do not work, consider contacting the manufacturer or a technician to fix it.

Why do batteries in my thermostat keep dying

The batteries in the thermostat keep dying because of several reasons:

Corroded contacts

Corrosion indicates a loose connection or high resistance short. It can affect the battery by speeding up the current or voltage and decreasing the amperage. A solution is to clean the corroded contacts to allow them to work well.

An old thermostat

Most thermostats do not have a set lifespan. But on average, you can expect your thermostat to last at least ten years. After this period, it will start malfunctioning because of aging wiring or dust accumulation. That can also cause constant draining of the battery.

Incorrect battery type

If you have replaced your battery recently, check to ensure you have purchased the correct one. Most thermostats recommend a voltage of 3.6. But if you have a 1.5V battery, expect it to drain quickly.


A low battery in a thermostat can affect it in different ways. It will prevent your house’s heating and cooling system from running effectively.

If there is a power outage, you will lose your energy-saving settings. You also risk the thermostat going blank, and you won’t have a way to adjust temperature settings.

Consider replacing the battery as soon as you see the warning to ensure your HVAC operates well. But when batteries in my thermostat keep dying after a short time, the problem could be an old system or an internal error.