what happens if thermostat battery died

Have you just installed a new thermostat on your premises and would wish to understand what happens if thermostat battery died?

Well, you are used to that cool and warm temperature, but suddenly it is not there. What has happened? Maybe the batteries have died.

Let us see below what happens if a thermostat battery dies.

If your thermostat battery dies, you will not be able to use the system. To get the unit back in order, you will need to replace the batteries.

What Happens if Thermostat Battery Died

Before going further, we may need to understand what happens when thermostat batteries die.

The plain fact is that your system will not cool or heat your room. You can only get back to your cool or hot room at specific times when you replace the batteries.

Do All Thermostats Need Batteries to Run?

Not all thermostats need batteries to run. Some only need to be hardwired into an electrical grid, and they are good to work.

However, most thermostats have batteries that back up your settings. So, in case there is no electricity, you will not lose the system’s settings.

Older thermostat models do not have batteries. However, most digital thermostats have batteries.

If yours has batteries and you do not change them when discharged, you will see a blank screen display, and the system will not function.

If replacing the batteries does not get the system back to work, you may need to reset the thermostat. However, resetting will always depend on how long it has been since you replaced the batteries.

Types Of Thermostats

Let us look at the different types of thermostats that have batteries but need a source of power for them to run.

1. C-Wire Thermostat

C-wire is the primary source that connects your thermostat to your home’s power supply. It has a batteries slot.

However, you only need them as a backup when there is a power outage.

So long as there is power, your C-wire thermostat will operate. But when the batteries are dead and there is no power, the system too will not work.

When you realize that the batteries are dead, kindly replace them lest you reset the system in case of a power outage.

The owner’s manuals will often help you know the kind of batteries your thermostat is compatible with.

2. Battery-Powered Thermostats

These types of thermostats depend entirely on batteries as their power source.

Anytime the batteries die, your system too will have no power. Also, when the batteries are weak, your system too will weaken.

Hence, it is essential to replace the batteries frequently. The good thing is that the system has an indicator that will often notify you when the batteries are low.

Another advantage is that the batteries will not die immediately the indictor shows low batteries.

The indicator will give you this information between one week and four weeks before the system powers down.

Which Signs Should Tell You that the Batteries Have Died or are About to Die?

signs thermostat battery died

When the batteries are weak, the cooling and heating system will not work properly.

When the batteries are preparing to die, you will often see some signs depending on the type of thermostat you have.

Some signs include:

  • Flashes on a battery-shaped indicator.
  • A shining LED light indicator next to the low battery.
  • The screen becomes dim.
  • A low-frequency audio alert, if your unit has one.
  • A malfunctioning HVAC system.

The solution is to constantly replace the batteries soonest, or anytime you begin to notice any of these signs.

How to Replace a Thermostat’s Battery

Replacing your thermostat’s batteries depends on your brand and model. Most thermostats have their batteries beneath them inside a panel.

You can find others in the thermostat’s faceplate back.

If yours are located in a panel, you will only need to open the panel, remove the batteries and replace them using the same direction.

If your batteries are behind the thermostat’s faceplate, use these step-by-step guides to replace them.

Step #1: Pull the Faceplate

The faceplate is clipped into place; you need to use some little strength to pull it out.

Step #2: Disconnect the Faceplate from The Power Source

After removing the faceplate, the wires behind it are still connected. We do not want to lose you! So, unplug it carefully from its power source.

Step #3: Change the Batteries

Locate the batteries behind the faceplate and remove them. Check which direction the batteries are facing, then replace them with new ones facing the same direction.

You will also see a diagram on the faceplate showing you how to position your batteries.

Step #4: Connect the Faceplate

Plug-in back the faceplate to the wall panel. Please do it carefully.

Step #5: Return the Faceplate

After plugging in the faceplate wires correctly, place the faceplate back to its position. Line up every corner and ensure it fixes well in place.

Step #6: Check the Thermostat’s Settings

After aligning everything, you may need to wait for about 30 seconds, and your thermostat will begin working.

Check the temperature settings and every other schedule. Your unit should be working well now if you did everything correctly.

If you feel like it is taking longer, you can reset the system.            

How Long Should a Thermostat Battery Last Before it Dies?

Two factors determine the life expectancy of your thermostat batteries. They include your device and its usage.

If your thermostat is newer, it may stay a bit longer with the batteries. An older thermostat may not last the batteries as long. As time goes by, the system wears down, and the batteries’ efficiency also decreases.

However, your batteries should operate at least eight months to 1 year before you think of replacing them.

What if your batteries drain so quickly than they should? It is not normal, and you may need to understand why it happens.

Reasons Why Batteries Die Quickly

There are a couple of reasons why your batteries die quickly, these include:

Your Thermostat Is Old

As your system wears down, it makes the batteries spend too much energy to run. So, it drains the batteries quickly.

There Is An Error In The System

The system’s wiring may be having some defects which cause the batteries to drain quicker.

If you notice that your thermostat batteries are dying out so quickly, maybe you are replacing them week after week, you may need to call a professional to check it for you.

They may need to replace the thermostat if it is too old or correct the wiring with the defect.

How to Lengthen Your Thermostat’s Batteries Life

Everyone wishes that their thermostat batteries last longer. Of course, no one wishes to spend on batteries only, yet there are other responsibilities.

To keep your batteries longer, you will need to keep things energy efficient.

Do not turn on and off your system every time. At times the system may have an issue, and it turns on and off each time, or you decide to power it on and off frequently.

Doing this makes the system malfunction completely.

Besides, when the system kicks on, it uses lots of energy hence draining the batteries quicker. It can also burn the system.

Please opt to replace the batteries at around 5 or 7 dollars instead of using thousands to replace the AC unit.

Read Next: How to Remove Old Honeywell Thermostat from Wall?


When your thermostat’s batteries die, you will see a blank screen. The unit will not heat or cool your room. To get it working again, replace the batteries.

I hope you now know what happens if thermostat battery died. No one may need to tell you that the batteries had died since your unit can indicate that for you.

Your screen will go blank, and the unit will not heat nor cool your room.

So, anytime you realize your battery is dead, replace them and get the system back to work.

Nicole B