Toyota Prius Smart Key: Battery Change & Lost Key Replacement Tips

In this article, we’ll show you tips to change the smart key battery and lost key replacement.

What Is A Smart Key / Key FOB?

Smart Key Battery Change & Lost Key Replacement Tips

A Smart Key is an advanced version of an automobile key. A Smart Key allows for keyless entry into your vehicle.

The car’s onboard computer can detect when the key is near the vehicle and will allow you entry into the vehicle without having to unlock your doors manually. The car can also detect the key while you are inside the automobile and models like the Toyota Prius are equipped with a push-button starting system. As long as the automobile key is in the vehicle, you can just push the start button to start the engine.

The smart key doesn’t need to be out and it doesn’t need to be inserted into the ignition. It can be in your purse, your pocket, in the cupholder, or anywhere within range of the onboard computer. Another benefit of smart keys is that your car won’t let you lock the smart key in the vehicle. It knows the key is there and will prevent the doors from locking.

Similarly, the smart key system will automatically lock your car doors once you get far enough away from the vehicle.

Smart Keys are also referred to as Keyless Entry Systems and you will often hear the key called a “Key Fob”, remote transmitter, or keyless entry.

What do I do if my Prius key battery dies?

  • You Are Locked Out Of Your Car
  • Your Smart Key Battery Is Dead

There is a manual key hidden inside the key fob.

Prius Smart Key Manual Key InsideIt is very important to learn how your smart key works, especially in times of distress. I find it odd the number of automobile owners that come into the dealership and have no clue how their smart key works.

People come in all the time and are surprised to find out that there is a battery and/or a manual key tucked inside the smart key fob. So I’ve decided to teach a little about the smart keys in hopes of preventing your readers from ending up like this poor lady.


In the image, you can see that there is a manual key that is hidden inside the Toyota Prius key fob. The image shows a new uncut key, but the one in your key fob will be cut to open the door of your vehicle. It is important to know where this key is located and how to remove it. Both are rather simple.

The keyring in the Toyota Prius smart key is attached to the hidden manual key. To remove it from the key fob base, just slide the tab on the end of the fob and hold it, while pulling on the key. It should slide out easily, although it may be a little stiff the first few times you remove it.

This manual key is designed to get you into your car, should the battery die in your smart key. This key is only designed to allow you to enter the vehicle, it will not start your car’s ignition.

Once you are inside, you should be able to use the remaining slight bit of battery life to get the car started. This will allow you to get to a location to get a new battery replacement. To start the ignition on the push-button starter, just hold the smart key fob up against the ignition button.

Push the ignition start button with the smart key as close to the ignition button as possible. You can actually use the smart key to push on the ignition instead of using your finger.

There should be just enough juice left in the battery to get your car started and allow you to reach your location to have the battery changed, whether it is an auto dealership or a retail store.

You are locked out because the battery signal is too weak to reach through the vehicle to the onboard computer, but should have enough signal for 1 or 2 more starts if you do as explained above.

To prevent all of these issues, just pay attention to the onboard screen in your car. It should tell you when your battery is getting low in your smart key. Just replace the batteries in the smart key once the warning light is indicated and you shouldn’t have to worry about being locked out of your smart car.

These Can Drain Your Smart Key Batteries


Do not store your smart key near any of the following devices or they can drain your battery.

  • TVs or Computer Monitors
  • DVD or VCR Units
  • Desktops PCs or Laptops
  • Cordless Phones or Cell Phones
  • Microwave Ovens & Other Electronic Cooking Appliances
  • Modems
  • Certain Lighting Fixtures

Note: Store Smart Keys at least 1 meter away from these items.

How do I change my Prius key battery?

Most smart keys, regardless of the make and model of the vehicle, have a small battery that is easily replaced. These batteries are commonly referred to as “watch batteries“. Don’t let the dealership make you think you can’t replace it yourself. Changing your smart key fob battery is actually pretty easy to do yourself if you know how to open the key fob.

Here at the Toyota dealership, we charge $12.50 to install the battery for you. Yeah, $12.50 for a watch battery that cost us $1.49. You can easily find the same batteries at places like Walgreens, Walmart, Best Buy, any other major retailer that sells batteries. has been the cheapest place that I have found them. The Smart Key batteries are so cheap at Amazon, that we’ve even started to order them from there to sell at a mark-up to our customers. At the chain stores, the battery will only cost you around $3 to $4 each, and getting a multipack will save you even more cash. Amazon has them for as low as 39 cents at times.

Since these smart keys are constantly on and searching for a signal, the batteries of each smart key fob tend to die at around the same time. So when you replace one, you might as well get a multi-pack and replace both smart key batteries together.

How To Change Your Prius Smart Key Battery

First, you need to remove the spare manual key that is tucked inside your key fob. This is done by locating the sliding tab on the end of the key fob. It’s on the end that the keyring is attached to.


By sliding the tab away from the keyring and holding it, you can pull the spare key out of the key fob base.

Once the key is out, you need to slide the same tab over and hold it, while sliding off the back of the casing.

Once the back is off, all you have to do is remove the 4 tiny screws that cover the battery plate. I highly recommend using a magnetic screwdriver to keep the screws attached to the screwdriver while you remove them.

This helps prevent dropping and losing the screws and also makes it much easier to put the screws back into the base once your battery is replaced.

Once the back is off, the battery can be popped out with another small screwdriver or anything else small enough to dislodge the battery.

Be careful: not to damage any of the internal components, as these smart key fobs are rather expensive to replace.

How Long Should A Smart Key Battery Last?

A New Smart Key Battery Should Last 2 to 3 Years.

Video of How to Change Your Prius Smart Key Battery

Here is a video that shows you how easy it is to replace your own smart key battery. Using just a precision screwdriver set and a replacement battery, it takes less than 5 minutes to replace the smart key’s internal battery.

Internal vs. External Key Cuts: What’s The Difference?

There are 2 types of key cuts for automobile ignition and door keys. Some automotive brands use both types of cuts and others use either the internal cuts or the external cuts.

When we think of the majority of keys, we think of an external key cut. Think of your house key. The key cuts are made into the outer edges of the key shank. Automobile keys have historically been made with external key cuts as well. Lately, more and more auto companies have been switching to the internal key cuts.

Toyota Prius Internal Key Cut

If you refer to the image, you will see an internal cut key for a Toyota Prius smart key. The newer models are using the internal cut key for the manual entry key, which is hidden inside the key fob. The main difference is that the cuts are made on the inside of the key, with the outer edges being smooth. Lexus has been using these internal cut keys for a while and now Toyota is starting to use them on many of their newer vehicle models as well. The main benefit of having an internal cut key is for security purposes, but they are more expensive than the external cut auto keys.

If your vehicle requires an internal cut, you are looking at adding around $100 extra to the cost of replacing your lost car keys. The reason is that these internal cut keys take an expensive high tech laser key cutting tool. These laser key cutters are so expensive that most dealers choose not to make the investment for their own laser key cutting machine. Therefore, most dealers will have to order your key pre-cut from the manufacturer. This increases the time required to complete your order and also raises the price. Unfortunately, you don’t have a choice on which key cut your vehicle uses. That is determined by the auto manufacturer’s make and model.

What do I do if I lost my Prius key?


Tips For Saving Cash & Frustration

Smart keys are rather expensive to replace. Most customers are completely shocked when they find out that a replacement key is going to cost them between $200-$400 each. The smart key hardware is pricey itself, but your new key will have to be programmed at a dealership. Not only does the keyless entry have to program and set to match your vehicle, but many keys these days have an immobilizer chipset within them. These also have to be programmed to match the onboard computer, which is also required to be programmed at the dealership using the dealer only key matching software. So you end up paying for the hardware (the key fob itself), as well as around an hour’s worth of labor for the programming.

What To Bring With You To Get A New Smart Key

When you need to get a smart key replaced and programmed be sure to bring the following:

1) The Vehicle – The vehicle must be present for the programming.

2) A Working Key – Without 1 working key to the program from, there will be an extra 30 – 60 minutes of labor added onto your bill. The master technician has to contact the manufacturer and get a special over-ride code and get permission to even perform the key programming. This can take an hour or longer on top of the hour of programming. That is if an override is available. With some models, you could be forced to replace the car’s onboard computer, which can be very expensive.

3) Make an appointment – You can’t just walk into a dealership to have a key programmed. Having an appointment ahead of time is required at most dealerships.

Some customers try to save money by buying the key fob online through eBay, Craigslist, or an online parts depot. This isn’t always the best idea though.

Write Down The Important Numbers Before You Lose Your Keys

Take Note Of These Numbers

  • MDL #
  • FCC #
  • IC #

Be Careful Buying Replacements Online


Be very careful when trying to save money by buying the key fob online. While it may seem like a good idea to save yourself some extra cash by bringing your own replacement key fob to get programmed, it often ends up being an additional wasted expense. Why? The majority of customers who bring in their own key fob that they purchased online, off someone on eBay, or Craiglist get sold the wrong product. The key fobs are a high tech advanced security piece of equipment. You can’t just buy one online and expect it to work. Even if you provide the correct year, make, & model, odds are the one you receive will not be programmable for your vehicle.

If you do decide to buy a replacement key fob online to have programmed to match your vehicle, you must be absolutely certain that you get the correct one that works for your vehicle. Here is how to tell if it will work.

On your existing smart key, before you lose the key fob, be sure to make a note of the detailed information listed on your smart key itself. There will be a sticker on either the inside or outside of your smart key. In the image, you can see the dark grey sticker located inside this key. It is visible after removing the sliding back off of the Toyota Prius key fob. Other smart keys may have the sticker on the outside or may have the information etched into the plastic material itself. Let me repeat: Take note of this information now before you lose your keys and can’t access this important information.

What you are looking for is the following 3 numbers:

MDL#, FCC#, & IC#

  • MDL: Model Number
  • FCC: Federal Communication Commission Number
  • IC: Manufacturer’s Universal Code

If you purchase an online smart key, in order for it to work you must purchase a new one with these exact same numbers. If these numbers do not match, your replacement will not be programmable to your vehicle. This is very important. If you are trying to buy a used key fob from someone, just have them locate the information on the key fob and read it to you. If all numbers match, then the key fob should work for your vehicle. If the numbers don’t match, then don’t waste your time or your money!

When comparing prices to the dealer’s prices, always remember to figure in the cost of shipping. I’m amazed at how many customers forget to calculate the shipping charge in their final price comparison.

More Toyota Accessories


Make sure to stop by the Official Toyota Page on Amazon and check the prices of any aftermarket parts, original equipment parts, or Toyota accessories before paying full retail or Toyota dealership prices.

Enter The Toyota Store Here

More Useful Hybrid Vehicle Links

The Toyota Prius Hybrid Family
There’s a Prius For Everyone. Learn about all the different Toyota Prius models.

Prius Chat
An Online Forum for Prius Owners & Shoppers.

The Prius Chat Podcast
A Podcast devoted to discussing Toyota’s top hybrid vehicles.

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