What Happens If A Thermostat Battery Died? (Find Out Now!)

what happens if thermostat battery died

Most thermostats today need electricity running to them, but they also need batteries to operate. Research shows seven out of ten homes have thermostats to control the cooling and heating. Everything has to work in check, and batteries are a part of the maintenance list.

Like most technology, if batteries are involved, they will give signs or warnings they are getting weak. It is critical to pay attention when these signs happen. It is also essential to know how and when to change the batteries.

If the thermostat battery died, there would be no power going to the thermostat. The thermostat will not work at all. When the batteries are weak, you will notice a difference in the heating and cooling system.

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Two Different Types of Thermostats with Batteries

There are two types of thermostats that need a source of power to run.

  1. Battery for back up only C-wire thermostat
  2. Thermostat with a battery needed for operation

1. Thermostat with C-Wire

This type of thermostat needs a C-wire as the primary source to work with your home’s main power supply. It has batteries but is only required as a backup system should the power go out. If power is going to the system, it will still operate with dead batteries but fail when the power goes out.

You will need to change out the batteries for the backup, or you may have to reset the thermostat again. Not doing so will discharge the system in a power surge or when the electricity fails. When changing the batteries, check with the owner’s manual to make sure you know the type of batteries needed.

2. Thermostat with Batteries Required for Operation

These thermostats work solely on batteries, so it is critical to keep up with the maintenance. If the batteries die, there is no power going to the system. When the batteries are weak, so to will the thermostat weaken.

There is a low battery indicator that will come on when the batteries are fixing to die. You will notice it showing one to four weeks before the system will discharge fully. It leaves plenty of time to detect in advance.

Does Every Thermostat have Batteries?

Older model thermostats and those that use the main power with the C-Wire’s assistance do not have batteries. Most digital thermostats have batteries. If you forget to change the batteries in those, the screen will go blank, and the unit will not work.

The simple fix is to change the batteries to fresh ones. In some thermostats, you have to reset them, depending on how long it has been discharged. Usually, after five or ten minutes, the thermostat will hold the saved programs.

The Signs the Thermostat Needs New Batteries

Weak batteries will cause errors in the heating and cooling system, and the thermostat will begin to act strange. Some thermostats have a battery-shaped digital showing that flashes when the batteries are weak. Others have a LED light indicator shining next to the “LOW BATTERY.”

These are some other indicators that will take place when the batteries are fixing to die.

  1. The screen will become dim.
  2. For those that have them, the audio alert volume will be at a low frequency.
  3. The air conditioner will malfunction due to a low voltage in the relay.

When these signs begin to become noticeable, replace the batteries as soon as possible.

How the Low Batteries Affect the AC Unit

There is a signal sent from the thermostat to the AC unit that controls the temperature. It tells when the unit runs and when to kick off. There is a relay switch that helps this process along.

If the batteries are weak, the thermostat’s low voltage to the relay may not make it to the unit. The AC will malfunction and may not even kick on.

The Different Types of Batteries Used in Thermostats

The two types of batteries used for thermostats are COIN Li-ion and Alkaline. It is not recommended to use lithium-ion batteries. Here is the list of the three different types of batteries used and how they function with the thermostat.

  1. AA Alkaline: It has a capacity of 2,400mAH with a typical drain of 50mA
  2. AAA Alkaline: It has a capacity of 1,000mAH with a typical drain of 10mA
  3. 3V COIN Li-ion: It has a capacity of 2,40mAH with a typical drain of 2.9mA

Why It Is Not Recommended To Use Lithium-ion Batteries

Alkaline batteries have significant reasons for use over lithium-ion batteries. Here are the four specific reasons.

  1. Alkaline batteries are Eco-friendly and do not have heavy metals that will pollute the groundwater or soil.
  2. Alkaline batteries offer sustainable output voltage 100 percent of the time.
  3. Alkaline batteries are not as expensive as lithium-ion batteries.
  4. Alkaline batteries operate more efficiently in warmer temperatures than lithium-ion batteries.

The Life Expectancy of Thermostat Batteries

The two factors that determine how long the batteries will last inside the thermostat are the usage and device. Newer thermostat devices will operate longer with fresh batteries, while the older models will not last as long. The battery efficiency will decrease over time as the more recent system wears down.

Common Reasons Thermostat Batteries Drain Quickly

There are a couple of reasons the batteries may die quickly after installation. When this happens, it is important to understand; this is not normal. If you notice you are changing out batteries week after week, get in touch with a professional.

Older thermostats will drain the battery, which is normal, but too quickly means the thermostat may completely give out. If there is an error, whether in the wiring or the digital system, it will also drain the batteries quickly. Those are the two most common reasons a technician will have to work on or replace the thermostat.

Keeping Things Energy Efficient

Most people do not realize this, but it takes a lot of power when the unit kicks on. Another reason for keeping up with the maintenance of the batteries is keeping things energy efficient. If the thermostat is not working correctly and the unit keeps kicking on and off, more electricity is being used.

Along with draining the batteries quicker, constant turning on and off can burn the AC unit over time. That is where the cost is apples and oranges, the batteries versus the AC unit. Two batteries cost about $5 to $7, while an AC unit repair or replacement can cost thousands.

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How Do You Replace the Batteries In a Thermostat?

It depends on each model or brand of the thermostat on how to change the batteries. The common places are under the thermostat inside the panel or in the back of the thermostat faceplate. If it is a panel, open the panel, take out the batteries, and replace them in the same direction.

Here are the steps to take if it is behind the faceplate. Honeywell and others like it are designed this way.

Step 1: Remove the Faceplate

Take the faceplate off the front of the thermostat. It should pull off because it is clipped into place.

Step 2: Unplug the Faceplate

After you remove the faceplate, the wires are still connected. You will need to unplug it from the wall carefully.

Step 3: Replace the Battery

Remove the old batteries from the back of the faceplate and install the new ones in their place. Take note before you remove the old batteries in which direction they are facing. If you forget, there should be a diagram showing the direction the new batteries go.

Note: For the COIN batteries, lift the old battery out and replace it with the new one. Make sure the metal over it is secure, so the battery remains in its proper place.

Step 4: Plug-In the Faceplate

Carefully plug in the faceplate back into the wall panel.

Step 5: Put the Faceplate Back On

Put the faceplate back on after the wires are plugged in. Line everything up and push it into the wall until everything clicks into place.

Step 6: Check Everything on the Thermostat

Once you have everything in place, it may take ten to 30 seconds before the thermostat comes on. Check all the schedules and temperature settings. If you did everything in the given time frame, everything should still be set.

You might have to reset the thermostat if it took longer than the grace period.

Upgraded Home Team

We are a team of passionate homeowners and home improvement enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and gardening tips with other homeowners! Whether you're looking for a step-by-step guide on fixing an appliance, cleaning your carpet, or even putting up a fence, we've got you covered.

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