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How to Change a 12V Prius Battery: 12V Battery Replacement


Dan is a "backyard mechanic" who has always done his own auto repairs whether on motorcycles, boats, cars, or even motorhomes.

How to install a new 12 volt battery in a Toyota Prius

How to install a new 12 volt battery in a Toyota Prius

Changing a Prius 12 Volt Battery

The Toyota Prius has two batteries in it; a large 200 volt battery that is used to drive the car in the electric mode and a small 12 volt battery that is used to operate the accessories such as lights, radio, etc. This article is written to show how to change the smaller, 12 volt battery.

Unlike most cars, this battery is not a very simple thing to change or install. It is buried in the trunk, not under the hood, and there are many items in the way of getting the work done. Nevertheless, it is not particularly difficult as long as you understand where it is and what needs to be done to give access to it. The task is well within the capabilities of the ordinary homeowner and should not require too much time to accomplish. The changeover shown in the photos was done in about ½ hour by someone fairly experienced in working on cars but that had never done a Prius battery change.

Like every car battery, the one in the Prius will wear out - it is normally good for around 5 to 6 years but can last longer. Unfortunately it loses it's strength when left in place too long and will go dead much quicker if the car isn't driven daily. An overage battery can also negatively affect the gas mileage your Prius will get as the car will continually attempt to charge it back to full status but the battery simply won't accept a full charge any more. That takes gas; gas that could be going into moving the car but is instead going into a futile attempt to charge a battery that is partially dead.

Finding a Replacement Battery for the Prius

The Prius battery is an unusual one - it is smaller than normal cars carry and a glass mat construction rather than the normal lead acid type. It can be purchased from a Toyota dealer, of course, but there is also one other option.

Just one company makes a battery that is a direct replacement for the Prius battery and it is considerably superior to the one from Toyota at about the same cost. That company is Optima, a well known battery manufacturer that produces top quality batteries, and the model number as of the time of this article is the Optima DS46B24R. This battery is a direct replacement for the 2004 and newer model Prius that is equipped with a smart key system, as most cars in that range are.

It is slightly too large for cars that are not equipped with the smart key; it fits into a depression in the trunk that in other models is just a bit too small. There is another Optima that is described as fitting into earlier models or cars without the smart key system, but this writer cannot guarantee that it will fit properly. That battery also requires some modification to the battery terminals to be used, and installation kits are available for that.

Make sure, then, that if you are purchasing one of the Optima batteries (highly recommended over the stock Prius battery from Toyota) that the correct model number of DS46B24R is purchased; while other models may fit without a special installation kit, they may not.

Update: Since the writing of this article, ACDelco, a part of General Motors, has begun offering these batteries as well. Amazon carries the ACDelco ACDB24R battery as well, and it, too, is an exact fit for the Prius in the years discussed, at a considerably lower price.

Tools to Remove the Prius Battery

There aren't a lot of tools necessary for this task; it just isn't that major. Make sure you have the following on hand, though:

  • Either a 1/4" or 3/8" drive ratchet.
  • An extension for the ratchet, about 5" long. A 3" is too short; an 8" probably too long.
  • 10 mm socket, preferable a deep socket
  • 12 mm socket, shallow or deep.
  • Large flat screwdriver or small crowbar. It will be used to spread the battery terminal for easy removal.
  • An old glove, rag or some other method to cover the battery terminal so that it doesn't short out on surrounding metal.

Removing the Prius Battery

Before starting the work you will need to decide whether you want to keep power to the vehicle at all times. Failure to do so is not a major problem but you will lose such information as the radio presets and power window limits if you don't maintain power. Neither is a big thing to correct - input the radio information again and run the windows up and down a few times.

If you want to avoid this small problem, you will need another battery (perhaps in another car) and jumper cables or a battery charger. Instructions are in the section below, and once the power source is connected you can proceed. Do take notice of the caution given there.

  • Open the hatchback and if you have a floor mat there, remove it. Remove the carpet and the cover over the hidden storage space.
  • Remove the plastic storage bin, exposing the spare tire.
  • The battery is located under a plastic molding on the far right, in the rear of the trunk. Unsnap the molding and remove it. This will expose the battery to view.
  • Crossing the top of the battery is a squarish air duct used to cool the primary drive battery. It is far too close to the battery to permit removal and must be removed before the battery can be taken out. There is a 10 mm bolt on the side of the car, behind the carpeting on the side, and another nearer the center of the car. Pull the carpeting up enough to reach the bolt and remove it as well as the second bolt; the duct can then be worked out and set aside.
  • It will be far easier if the brake controller, just to the inside of the car from the battery, is moved aside. There are three 12 mm bolts holding it; remove those bolts and carefully swing it aside and out of the way. There will still be wires attached to it, so take care not to tug hard on those wires.
  • Remove the positive cable from the battery, including the plastic housing over the terminal. Loosen the 10 mm bolt and, with a screwdriver or small pry bar, open the terminal a small amount. Lift the terminal straight up, being very careful not to allow it to touch any part of the car. Cover it with an old glove or wrap a rag around it to prevent shorting to the car body and set it out of the way.
  • Remove the battery hold down, a bar across the top of the battery. There is a 10 mm bolt on one side and a 10 mm nut on the other; take them both out and remove the hold down.
  • It will be easier to remove the negative terminal from the car body rather than from the battery. There is a 10 mm bolt holding it to the car, and that bolt is much easier to reach than the bolt on the terminal itself. Remove that bolt and fold the wire over the battery.
  • There is a vent tube on the forward side of the battery. Pull the tube straight out of the battery and, without pulling it from the car, set it out of the way.
  • Lift the battery out of the car and remove the negative battery terminal and wire from the battery. Take notice of how it is pointed before removing.

You are ready to install the new 12 volt Prius battery.

Keeping Power to the Car

While not absolutely necessary, it will be advantageous to keep some power to the car during the battery change in order to keep the settings on the radio and windows.

To do this, open the hood. On the far drivers side is the fuse box; pop the lid open. Inside is a large red plastic cover over the positive jump start terminal. Remove the plastic cover.

Connect either a battery charger or jumper cables from another battery or car. The positive wire goes to the bolt terminal under the plastic cap, the negative (black) wire can be clamped to a nearby bolt head on the body near the windshield

Caution! Connecting the wires backwards may cause several thousand (yes, thousand) dollars worth of damage to the electronics of the car. Make absolutely certain that you know which wire goes where before making any connections! Your Prius manual has further directions; the wires are to be connected exactly as if you were going to jump start the car.

Installing the New Prius 12 Volt Battery

Installation of the new battery is a reversal of the steps already taken.

  • Install the negative terminal wire onto the new battery, making sure it is pointed in the same direction as it was on the old battery.
  • Set the battery into the floor cavity, with the positive terminal towards the front of the car.
  • Bolt the negative terminal to the car body.
  • Set the hold down bar into place and bolt it down. Just snug the bolt and nut; excessive tightening will do nothing but bend the bar and could, if grossly over-tightened, crack the battery.
  • Attach the positive terminal assembly, being careful not to twist the wires from the position they were in originally.
  • Replace the vent tube by pressing it into the hole in the side of the battery.
  • Replace and bolt the cooling vent for the main battery pack.
  • Replace brake controller, bolting it all three locations.

Now is a good time to remove the jumper battery or battery charger, if used, and test start the car. If it does not start, carefully check that the positive and negative wires are in the correct location on the battery and, if necessary, provide a jump start. Once you have started the car, turn it back off and the rest of the installation can continue.

  • Replace the plastic molding covering the battery assembly.
  • Replace the hidden storage over the spare tire.
  • Replace the flooring over the storage area.
  • Replace both carpet and any floor mats.
  • Disconnect the jumper battery or battery charger, if used, in the engine compartment.

Most batteries will come with sufficient charge in them to start up the electronics of the Prius, but will need additional charging before long. You will need to take the car for a short drive, a few miles, as soon as convenient.

The new battery.  The negative wire is attached and it is ready to set into place.

The new battery. The negative wire is attached and it is ready to set into place.

Ready to go?

For each question, choose the best answer. The answer key is below.

  1. Voltage from a spare battery must be maintained at all times
    • True. Power to the fancy electronics must never be removed
    • False. It is quite acceptable to remove all power from the car
  2. The battery is located under the hood
    • True - it is near the from passenger tire
    • False - it is in the trunk, on the passenger side
  3. Care must be taken to avoid touchng the positive terminal to the body of the car
    • True. Never touch the positive terminal to anything but the battery positive.
    • False - it will not hurt anything
  4. The battery is under the floor
    • True. The floor and hidden storage compartment must be removed.
    • False. It is under the back seat.
  5. The job should take around 3 hours
    • True. This is a complex and difficult task.
    • False, This is an easy task and should be done in less than 1 hour
  6. The new battery must be purchased from Toyota
    • True. There are no aftermarket batteries for the Prius
    • False. Optima makes a direct replacement, although it will probably need to be ordered online.

Answer Key

  1. False. It is quite acceptable to remove all power from the car
  2. False - it is in the trunk, on the passenger side
  3. True. Never touch the positive terminal to anything but the battery positive.
  4. True. The floor and hidden storage compartment must be removed.
  5. False, This is an easy task and should be done in less than 1 hour
  6. False. Optima makes a direct replacement, although it will probably need to be ordered online.

If you're satisfied with the results of the quiz, it's time to start the project. Return to the beginning and carefully follow each step. You will save yourself around $100 by doing the work yourself.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: Will a Prius start with a dead 12-volt battery?

Answer: Only with a jumper battery or car attached. It requires that 23V supply to start.

Question: Does a 2009 Prius need to be reprogrammed after a new battery is replaced?

Answer: If you disconnect all sources of 12V power to the car a few things will need re-programmed, such as the windows and radio settings. They are all very simple (run the windows up and down, input the desired radio stations, etc.) and there is nothing that will keep the car from operating fine. (I'm assuming you refer to the small 12V battery, not the one that moves the car.)

Question: How do I reprogram a 2012 Toyota Prius?

Answer: If all you need is new radio presets and window controls, put them into the radio and run the windows up and down a few times. There should be nothing more than that from simply changing a battery.

Question: Can a 12V battery overnight charger be used to recharge a Prius?

Answer: A normal automotive battery charger can be used to recharge the 12V battery in a Prius. It cannot be used to recharge the large high voltage battery that moves the car.

Question: How do I check my 12v battery voltage?

Answer: Using a volt meter, check between the "jumper" connection under the hood and a good ground. With the engine off turn on the headlights for 10 minutes and re-check. Both times it should be 12V or a little more.

© 2013 Dan Harmon


Dan Harmon (author) from Boise, Idaho on August 21, 2020:


If there is enough charge in the 12V battery to kick on the electronics you should be able to turn the car on and charge the battery overnight. Of course, if there is that much charge you could do the same thing by simply driving it.

But removing the positive (or negative) cable from the battery will prevent any charging at all.

Dennis Taggart on August 20, 2020:

Is it possible to charge the battery overnight using a car mains battery charger without having to remove the battery itself. If so would I need to disconnect the positive and negative terminals from the battery.

Dan Harmon (author) from Boise, Idaho on July 02, 2020:


Ordinary batteries will not fit into the space, do not have the vent tube to vent hydrogen gas from the car and use a slightly different charger. So no, an ordinary battery is not recommended.

kam on July 02, 2020:

Can the 12 V Auxiliary battery be replaced with any ordinary Lead acid New but cheap battery, say from Walmart.? Does it have to be the special , Absorbed_Glass_Mat type ?

Dan Harmon (author) from Boise, Idaho on April 28, 2020:


You can try locking the doors with the remote. Other than that, I'm afraid I have no suggestions. You may need a Toyota mechanic.

Nashid Khela on April 27, 2020:

I had a flat battery, opened the driver door wit the spare key, and crept to open the backdoor, was not successful, so disconnected cables and charged in site. On reconnecting cables the alarm goes off. Any advice

Patricia on April 23, 2020:

@ Ace - did you ever figure out the problem?

I'm currently having the same problem

Dan Harmon (author) from Boise, Idaho on February 15, 2020:

No, the battery is not 16V, although it should read a little above 12V. Automotive batteries are all just over 2V per cell; 6 cells gives 12V.

Andreas Hagen on February 14, 2020:

1. I'm not a mechanic, or even an auto sparky so use with a pinch of salt,

2. I only know my 2010 prius nothing else

But could swear my aux battery was 16v not 12v believe you are measuring on the wrong side of the circuit! or atleast was 15.25 and is now 15.75volts according to my multimeter. Now the ignition is working again, after mains charging. The battery man wanted me to replace the battery for 300$ wtf. Figured this out while installing tvs in my car. For your reference only.

Rick Hanton on December 31, 2019:

Thanks for the awesome instructions! Worked like a charm. It's also easy to check the battery voltage using a cheap cigarette lighter checker or the car's diagnostic menu (turn on + hold "Display" + lights on/off 3 times).

Dan Harmon (author) from Boise, Idaho on December 23, 2019:


You may need a mechanic to diagnose the problem. It sounds like the main relays are not clicking in for some reason. The lights will be running off of the 12 volt battery, which indicates it has plenty of power but it still isn't coming on.

Ace on December 23, 2019:

Hi, I have been having some troubles with my toyota prius 2005 in that it will not start so I replaced the battery with a new 12v. After installation, the car will still not start, but the lights work fine. What is the problem?

Dan Harmon (author) from Boise, Idaho on October 25, 2019:

LOL That's pretty common - it takes longer to find the tools than to do the job!

thwart on October 25, 2019:

Thanks very much for the information here! Gave me the confidence to tackle this myself even though I don't generally do car repairs.

Just changed the battery on my wife's 2012 Prius V. It was actually easier than I thought, and a bit simpler than illustrated here.

No brake controller to deal with, and the negative terminal was bolted to the rear panel so access was very good.

Took me 30 minutes or so... and a good part of that was finding my battery charger.

Dan Harmon (author) from Boise, Idaho on August 03, 2019:

If you have access to another 12 volt battery, any size for any car, it could be mounted and wired temporarily to see if it will hold a charge. Perhaps install it with only a partial charge.

Start the car and run it for a while, both sitting still and operating. Turn the car off and on several times. If the temporary battery is in good shape with a good charge then the charging system is good. If it loses charge then the problem is somewhere besides the battery.

Sha on August 03, 2019:

Hi, 12v battery totally dead on a Prius I bought it like this. It jump starts and runs good though, I drove it for an hour but the 12v battery doesn't hold chrage at all. How to check if the charger or electric motor to 12v battery is defective? As you replied to one of the questions to Linda LK about the possibilty of defective charger or electric motor. The 12v battery is not cheap and if the problem is somewhere else then it's useless to replace it. Thanks

Dan Harmon (author) from Boise, Idaho on June 30, 2019:

@ Thomas Frazier:

Yes, it is much easier if the brake controller is removed as described. It's well worth the couple of minutes required to do so.

Thanks for the comment and glad to hear the job went so smooth.

Thomas Frazier on June 30, 2019:

On my 2007 Prius, I had to remove the brake controller prior to removing the air duct. At least, it was much easier that way. Great article, gave me all the info I needed and the job went smoothly.

Dan Harmon (author) from Boise, Idaho on January 16, 2019:

@Ryan: Good to hear it all went well. Yes, if that little battery is completely dead you would have to have a jump to get the trunk open.

Ryan on January 16, 2019:

Thanks for taking the time to share this, it worked great and care is back up and running. The battery had died all the way so I did have to hook it up to another battery to get the trunk to open.

Dan Harmon (author) from Boise, Idaho on November 20, 2018:


Either the new battery is not hooked up correctly or it is completely dead. Make sure the terminals are tight and that the (-) terminal is going to the ground of the car body. If that doesn't solve it you can jump start it with another car - instructions are in your car manual.

Josh on November 20, 2018:

I just changed mine, but the car will not start, not even the lights come on. What could be the deal? Did I install it wrong? Is the new battery dead? I got it from Toyota. $213.

Dan Harmon (author) from Boise, Idaho on April 02, 2018:

It might be acidic. You might check the drain line for being clogged and inspect the old battery for cracks. I'd clean up the water and sponge it down with a baking soda solution, then wash thoroughly just in case. Acid is not something you want sitting there, rotting out the sheet metal.

Dave on April 02, 2018:

Everything came out great. Found two inches of Water under the battery. Wondering why. Could it be acidic?

jack on November 07, 2017:

Thanks for the instruction. It sure made replacing the battery much simpler.

Dan Harmon (author) from Boise, Idaho on April 18, 2017:

I doubt the main battery was damaged by running the car on a dead or nearly dead 12 V battery. Could be the charger for the 12 V battery, could be a sensor somewhere or even one of the electric motors. I'd have to say to take it to a Toyota dealer. Sorry I can't help you more.

Linda LK on April 18, 2017:

12 volt battery replaced. Now inside lights dim with headlights on and cell battery not recharging well.

I did notice decreasing mpg from 49-46 prior to failure. I now get 57-58 mpg. Could the Cell batteries have been damaged by running car on dead battery or during installation, some issue that is causing the cell battery to be engaged to the point of poor recharging?

Dan Harmon (author) from Boise, Idaho on May 03, 2016:

Removing the negative cable first makes it less likely that the positive cable will short against a ground (body). However, in the case of the Prius there is the second, drive, batter to consider, along with the electronics to charge the smaller battery. At least some of this will be grounded as well, meaning that touching the positive cable to the body even after the negative cable is removed will likely produce a large spark.

macondo100 on May 03, 2016:

When removing the battery, don't you always want to disconnect the negative terminal from the car body first and then disconnect the positive terminal?

Dan Harmon (author) from Boise, Idaho on February 08, 2016:

You might try it and see if it starts the car, but that would not be proof that it's OK - it could be broken inside and making electrical contact until it vibrates a little and loses it. I would be afraid to depend on it, but if there is a way to use it safely for a month or two (carry a second battery and some jumper cables?) I'd be happier.

It's also possible that it was defective from the manufacturer - it should have taken considerable effort to bend that terminal. Although I've seen terminals damaged on other batteries with hammers or pry bars, the small wrench used to loosen or tighten that terminal nut should have been unable to bend it.

karmakid64 on February 08, 2016:

i purchased the new optima and i bent the negative post it did not take a lot of strength to bend i think it was too easy to bend. My question is: is the battery now bad? i think i may have heard a little air escaping. ugh i hope i didn't break it.

Dan Harmon (author) from Boise, Idaho on February 11, 2015:

Can you re-state your question? Not sure what you mean by "ran out" - both the Prius C batteries are charged every time the car is ran.

peachy from Home Sweet Home on February 11, 2015:

prius c battery is dry type right? How long do you use it before it ran out?

Dan Harmon (author) from Boise, Idaho on April 23, 2014:

No. There should be no connection between replacing the 12 volt battery and the smart key system. Certainly not in a simple reduction in range. Nearly a year after replacing the battery, I am also seeing a reduction in range of the electronic key but only one of them - the other works fine. If the battery change was at fault somehow both keys would be affected.

I suggest another key battery replacement and if that fails to help, another key. Expensive at around $200 but it might be worth it.

ThePaz on April 22, 2014:

When our 12 volt battery died after 6 years of use in our 2008 Toyota Prius we had it replaced. Now we're having problems with the electronic key working as well as it has in the past. We replaced the battery in the electronic key but the problem persists. My wife would go shopping & when she approached the car with the electronic key in her pocket the doors wouldn't open when you came in close proximity to the vehicle as it had in the past. Does replacement of a 12 volt battery require something being done so the electronic key works properly?

Dan Harmon (author) from Boise, Idaho on February 02, 2014:

Good point. As long as that positive wire is attached to the battery, any wrench used to loosen becomes positively charged as well and could short out if touched to the car body. It is wise to insulate it so that it cannot short if it is inadvertently touch to the body.

Thank you! on February 02, 2014:

THANK YOU. So much...the photos marked with the bolts were especially useful.

You might want to add that you also have to disconnect the bolt holding the positive wire to the pole - I knew that, but people who haven't changed a battery might not. They also need to know NOT to allow any metal tool sitting on that bolt to make contact with the car body - I wrapped a sock around the metal brake controller bracket at the back of the car, or you could use a rubber cover for your socket handle if you have one.

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