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Why The Toyota Prius 12v Auxiliary Battery Costs So Much

If you have been shopping for a 12v battery for your Prius you know how much they cost. The question is why are they so much? Here is what you need to know about your auxiliary battery.


If you have been a victim of 12v battery prices, I feel you. I have purchased many "special" batteries for my Prius' and each time about choked at the cost.

Why on earth would Toyota make such an expensive battery for these cars if all they are going to do is die anyway? Well, here are a few things you need to know about that battery and why it is so darn expensive.

Why Your Prius 12v Battery Is Different
Many do not know that the 12v battery in your Prius is different; they only know it is expensive. The 12v battery in Prius is a different animal and for a good reason. Toyota wanted to have a battery that could handle the type of use that these batteries get.

AGM or Absorbed Glass Mat batteries are built very differently than a typical lead-acid battery. With AGM batteries, there is no "free" liquid electrolyte. The "mats" inside the cell hold all the electrolytes. This action makes the battery non-spillable and much safer. AGM batteries perform better than "flooded" (lead-acid) batteries in applications where maintenance is difficult to implement. AGM also has minimal gassing when charging, making it a safer choice in many forms.

2010 Toyota Prius AGM battery

Safety is not the only reason that Toyota used them in Prius. Because Prius only needs to have the onboard computers turned on to "ready" on, the load placed on the 12v is very minimal. AGM batteries are better in this regard to be able to wear better over time because they do not need to be cycled like flooded batteries do to stay at peak operating performance.

Also, the onboard charging system for Prius Generations 1, 2, 3 was designed for AGM, not lead-acid. That means when the 12v is undergoing charge, the onboard computer is looking for a specific internal resistance of an AGM battery. SO if you put in a flooded style, it will not charge that battery correctly, and it will fail.

Internal resistance also plays a critical role in what battery you should buy. The Toyota batteries you get from the dealership are certified by Toyota to have the right internal resistance that will allow for proper charging. It has taken years for the aftermarket to start to get their Prius replacement batteries with the correct resistance values. Many new aftermarket Prius batteries would fail early on due to poor product design.

The aftermarket AGM would not charge the same way as the Toyota battery, and it would often undercharge or overcharge shortening the life of the battery.

So, AGM batteries are different, but why do they cost more? Excellent question.

Why Do AGM Batteries Cost More Than Flooded?
AGM batteries cost more than flooded due to several factors. The material cost for AGM is much higher. The glass mats that are in the cells are harder to produce than lead-acid separator plates. Lead-acid is also far easier to recycle than AGM. These added costs get passed down to the consumer, and then we have a $200 battery.

With higher manufacturing costs and the fact they are harder to recycle, the makers of these batteries have to recoup their investment somehow.

Toyota Prius AGM battery

The higher cost does give you benefits, though. For starters, AGM is vibration-resistant battery technology. Where the battery rides in our Prius, it is subject to a lot of road vibration and shaking. A standard lead-acid battery would have failure faster as they cannot handle the jarring and shaking like AGM can.

AGM is found on other applications, too, like power sports. Because of how robust it is when getting hammered at the dunes or on a trail. It is also more resilient to freezing temperatures when the state of charge is low. Overall, it is a superior battery for our Prius'.

The batteries cost more because they give more. Plain and simple. Can you use a lead-acid battery in your Prius? Sure can but do not expect the same level of performance from it. That is a mistake you do not want to have.

If you get a Toyota battery, which you should, it will probably last at least five years. So 200/5 = 40. So every year you have your battery over five years, the less it ends up costing you. Suck it up, buy the right battery and move on. You will have far fewer headaches, and guess what? Your Prius will work the way it is supposed to as well.

Thank you all for reading. I look forward to seeing you in the next story. Why I Want A Toyota Rav4 Hybrid More Than A Prius AWD-e.

Watch this Toyota Prius truck with a nice little bed and click to subscribe to Torque News Youtube for daily automotive news analysis.

Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter is also an Instructor of Automotive Technology at Columbia Basin College. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter. Find his page on Facebook at Certified Auto Consulting. Read more of Peter's stories at Toyota news coverage on Torque News. Search Toyota Prius Torque News for more in depth Prius coverage from our reporters.


George (not verified)    May 14, 2020 - 3:43PM

Hi i have replace my battery with one yasha!do this make any trouble to my 2010 prius at electic or at any part in my car?thanks

Kurt (not verified)    May 16, 2020 - 12:26AM

I have 400 k on my 05 Prius with 2 optimum AGM battery replacements. I am an electrical engineer and replaced the failed AGM batteries with a $40 riding lawn mower battery a couple years ago and it is still working fine. Simple install adding vent tubes down and a 90 degree bend on 1 stock terminal.

Alex Tworkowski (not verified)    February 7, 2022 - 3:10AM

In reply to by Kurt (not verified)

Question: Why do a lot of batteries for the gen 2 prius say "For smart key only"? I don't see what the key has to do with the battery and they all seem to say that. My Prius does not have a smart key (or what they call Proximity key). Should I ignore all that? Thank you for your knowledge.

Asd (not verified)    February 15, 2023 - 8:15AM

In reply to by Kurt (not verified)

I bought Walmart AGM 24 f battery AGM it rremed my display and engine not stop by even pushing power off,it is 70 ah AGM battery.what should I do?
I know non AGM battery is not charged in Prius,how were you able to keep lawn mower battery charged,or you used lawn mower AGM battery?

Mi (not verified)    May 16, 2020 - 12:35AM

Also make sure to shop around different local Toyota dealerships. Some charge a lot more than others for the exact same thing. I bought one for my 2012 Prius for 197.00 at one dealership, the other wanted 237.00

Adofus Rex (not verified)    May 16, 2020 - 4:00AM

I think you fell for Toyota's BS on this one. AGM is cheap to produce, just look at eBay Amazon or AliBaba listings. The voltage is very close to flooded cell also.

Andy (not verified)    May 16, 2020 - 8:53AM

Hard to believe the Prius battery in rear corner suffers any more vibration/shock than normal underhood corner location. I did get a good deal at Batteries+Bulbs. Shop around; avoid dealer price gouging.

AndyP (not verified)    May 16, 2020 - 8:54AM

Hard to believe the Prius battery in rear corner suffers any more vibration/shock than normal underhood corner location. I did get a good deal at Batteries+Bulbs. Shop around; avoid dealer price gouging.

Peter (not verified)    May 16, 2020 - 2:44PM

You can use any glass mat battery that fits in there and has a vent tube connection. I have used a couple of aftermarket batteries fitting this criteria. Obviously 12volt and required amp rating same as factory. I have owned many Pruises over the years and never had a problem.

Jimi.A (not verified)    May 16, 2020 - 9:20PM

OK, the article has good content.
An AGM battery is better in this service, in the passenger compartment.

However, it will have reasonable life expectancy, if not much longer, only if it is charged properly.
The system design missed that function. A moderate float charge is applied when the system is on [Ready].
An AGM battery will do much better if it has an automatic charger with an AGM charging curve programmed in. This is a higher voltage than wet cells. Once a lead acid battery is fully charged, the charger needs to be turned OFF, otherwise the battery will be overcharged. That is why the 12v system is lower, because it is continuous. Put a smart charger on once a month, the battery will take a nice charge & be happy, and see how long that lasts! ;=)

Tim_Wit (not verified)    June 18, 2020 - 11:54AM

I ran across this article because my 12 volt battery in my Prius is now failing.
I have 310,000 miles on my 2007 Prius. The battery is the original battery; I am the original owner.

There is something to be said about OEM parts. Yes, you can buy parts cheaper, but they are most often cheaper parts and inferior in many ways.

The author makes a valid point about a $200 battery that lasts 5 years = $40 per year. And that may be what a cheap battery will last, if even that long.

Considering my OEM battery lasted 13 years, I think I'll stay with what has worked and worked well. Of course, I'll still shop around for its best price!

PHONG TO (not verified)    June 26, 2020 - 1:22AM

I replaced mine with a Champion lawn mower lead acid battery ($50). I used a scrap piece of 2x4 and some bolts to secure everything down and to affix the cables. Lasted 2.5 years. We've had some 100 degree days so I think it was the heat that killed it. But after reading this article I'm thinking about going AGM. Guess I'll order it from Amazon for $60.

Tom (not verified)    November 20, 2020 - 2:38PM

Wow! Very insightful! I was mad when the dealer asked me hefty for replacement! Thanks for easy explanation!

Rey Maldonado (not verified)    December 13, 2020 - 2:01PM

Is the Toyota OEM AGM battery for the 05 Prius AGM flat plate? or AGM spiral cell? I use a digital battery tester and I need to know this in order to get an accurate test reading

James T Carlet (not verified)    August 15, 2021 - 11:13AM

Just replaced the Panasonic D23 battery in my 2017 Highlander Hybrid with a Diehard AGM 35. No listing on the D23 but prices I saw for OEM were $300 plus versus about $200 for the Premium Diehard. Best part is an AGM 35 is readily available in case I am needing a new battery in Western KS in the middle of a blizzard with no Toyota dealer within miles.

Tony (not verified)    November 13, 2022 - 6:30PM

In reply to by James T Carlet (not verified)

Looking to replace the Panasonic D23 on my 2018 Highlander Hybrid. Have you had any issues with the AGM 35? Did you have to plug an extra vent hole?

Tomas Greene (not verified)    August 23, 2021 - 3:02PM

I just replaced the original battery which lasted 11 years!
So paying USD 200 for a new one is more than reasonable
Kind regards from Chile

Bob (not verified)    October 17, 2021 - 3:22PM

I’ve been waiting 6 weeks thus far for a Toyota 12V battery replacement (a H4) for our 2017 Prius Prime. Our dealer has graciously provided us with a loaner, free of charge, but they have no idea when Toyota will provide a replacement. Are such delays common? Why? Outlook?

RAH (not verified)    January 7, 2022 - 7:41AM

I have a 2011Prius with 237,000 miles and still using the original factory battery. Never a failure. Cleaned the EGR valve. Has better pick up go. Replaced PCV valve. No more oil consumption.

Alain (not verified)    April 17, 2022 - 9:48PM

In reply to by RAH (not verified)

good job on the EGP cleaning (mine clogged pretty good) and PCV replacement. I did the same on my 2014 Prius with 185k (150k then) - mine wasn't burning oil but I added an oil catch can to keep it all clean.
As for battery I just replaced mine (Interstate AGM) only because I completely drained it doing some ABS diagnostics (changing break fluid) otherwise I might had a couple more years. 8.3y isn't bad.
And the article is misleading - they cost more (3x) because they are not sold at costco and other places, and not standard terminal, so a niche thing. The same size 51 group lead acid is $80 at Costco vs 200-240 at dealer or other vendor.