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By Peter Neilson Jul 17 2019 - 12:34am

The Best 12v Battery Option For Toyota Prius

It will more than likely take you by surprise, but the day will come. You will get in your Toyota Prius and it will not be ready to go. The 12v will be dead, and you will be left thinking about what to do next. Lucky for you, I have the answer.
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I take great pride in learning more about the spaceship we call Toyota Prius. I especially love writing about how to keep them maintained properly, and what to do when parts need replacing.

A common issue that many Prius owners face all the time is that blasted 12v battery. It always seems that the 12v is going dead, or causing issues with our cars. I want to take a look into why this is and what you best replacement option is when it comes to taking care of the problem.

I have been at Weber State University this week studying with Professor John Kelly who has become a YouTube sensation for his work on hybrid and electric vehicles. I was able to chat with him at length about problems with the 12v system and why people are having issues with them. His responses were astounding.

AGM vs Lead Acid

Absorbed Glass Mat or AGM batteries are in all years of Toyota Prius. The only exception to this is Prius Prime. The reason they are used in our cars over lead acid batteries is because they do not spill. In the even of an accident the battery acid could leak in a regular battery and cause issues with getting acid all over next to the high voltage in your trunk. AGM is also a battery that can take abuse and keep on working, it is also better in extreme climates as well. The downside is one of these can easily run you between $150 to $235 depending where you get it from.

Lead Acid on the other hand is cheaper and still gets the job done, however due to the differences in the makeup of the batteries the charging system on the Prius is designed to charge an AGM battery, not a Lead Acid. This means that even though a Lead Acid may work, your car will not charge it properly and it will fail sooner than you want it too. So while it may seem the LA battery is the cheaper option, you may end up spending more over time vs getting the right battery for the right job.

According to Prof. Kelly, if you want the vehicle to function as designed, use what battery is required for the car.

Choosing The Right AGM

While talking to John, I relayed to him that at my school we have a 2004 Prius with a 12v battery that keeps going dead. I told him we spent quite a bit of money on our yellow top optima. He chuckled and proceeded to tell me that not all AGM batteries are created equal.

The Toyota Prius battery from the dealer can easily run you upwards of $235 dollars. For a battery that hardly does more than power up some computers and allow the high voltage system to come on, this can seem like a lot. In fact, that it just about all it does, really. It does not get used all that much. This is one reason that these batteries fail. They just are not maintained as well as they probably should be.

There is also another side to this story, and it is one I have been dying to tell everyone. The aftermarket batteries we are buying at autozone, walmart or wherever are not being built to the same standards as the Toyota OE ones. This means that the internal resistance of each battery, even though it is for Prius, will not yield the same results as the one you get from the dealer.

Three batteries that I looked at were from Autozone, O'reilly and NAPA. Each one has a 3 year warranty and all cost between $199 and $237 dollars. The Toyota Truestart battery runs between $176 dollars and $237 which is basically the same as aftermarket. It also carries a similar warranty as well. I am sure you can see where I am going with this.

Conclusion

It may seem silly to spend that kind of money on a 12v battery and especially one from your local Toyota dealer. However, if you are a Prius enthusiast like myself, you should be able to see that the right battery for your car is the Toyota Truestart AGM battery. It is designed to charge and discharge at the optimal rate that your Prius monitors with the DC-DC converter.

Just like choosing the right brake pads for your Prius will save you in the long run, the right battery will give you the right results.

I hope that you have enjoyed reading about new Prius Technology. Check out my other story 3 Top Tire Brands You Should Consider For Your Toyota Prius to find even more ways to make that fuel sipper go the extra mile.

Also Watch 5 Things To Know About Toyota Prius Battery Maintain it Well and Click to Subscribe to Torque News Youtube Channel for Daily Toyota Prius and Automotive News.

Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He is an automotive technology instructor at Columbia Basin College. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter can be reached on Linkedin and at Certified Consulting.

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Comments

Lazarus wrote on July 17, 2019 - 6:35pm
For background I bought my 2005 Prius in 2007 and I am still driving it on the battery I replaced in 2009, including starting in cold upstate NY winters. The reason is simple I tweaked the rules. Oh, I don't have that many miles only 170,000 and climbing. The secret is two fold. First, I agree about battery quality and that it needs to be an AGM but also I noticed something else, the amp/hour capacity of the stock battery is insufficient. The Prius is never truly shut down. At best consider it on standby. I installed the largest capacity AGM I could fit. Now remember, the 12v system runs computers, not starter motors so it needs to be a deep cycle type of battery, not one with high cranking power so I went looking for batteries that drive audio systems not cars. They are about half the price of the automotive ones with all the same safety features and construction. Second, I looked at the issue of cold temp power loss and the the rate of consumption while parked. I installed 2 window solar panels that recharge the 12v with a 7 watt trickle chargers in the back window. They were made by Voltzwagon to act as battery sustainers on their cars being shipped from and we're available at that time. The solar panels provide a trickle charger while parked in the sun. That charge offsets load while parked and warms the battery internally in winter without overheating it in summer. The same battery is still starting reliably every time 10 years later. Part of the failure of the battery is clever planned obsolescence that can be beat.
James Wendte wrote on July 18, 2019 - 4:29pm
So what battery did you put in? Could you please tell us?
Lazarus wrote on July 18, 2019 - 6:31pm
I believe I bought a VMax AGM 12v MB857-35 group 1 deep cycle battery meant for solar photovoltaic storage and portable DJ use. I have to go dig into the back to confirm it. I remember wanting one of the golf cart 55 amp/hr types but the physical size was too big. Remember that this is not a real automotive application, it's an electronics application and a true deep cycle is better if you're parked for any length of time and don't drive enough to fully recharge the battery. From Toyota's perspective an engineer would apply the minimum weight, capacity, and cost required to run the car and meet warranty requirements. They also love the fact that very few automotive battery manufacturers compete in that class so then they can dominate the parts replacement in an esoteric market. It's basic business logic not a conspiracy. 'The business of business is business.'
Cedric Ranada wrote on December 30, 2019 - 3:24pm
Hi I like your idea on using the Vmax AGM battery! How did you modify the battery posts to make the battery cables fit?
Dominic wrote on March 5, 2020 - 12:06pm
Lazarus, how did you modify the battery posts to make the battery cables fit?
Lazarus wrote on July 18, 2019 - 6:38pm
BTW, on re-reading my posts I apologise for not proofing and editing. I'm writing on my phone and noticed that at times it is autocorrecting things weirdly. If you want more follow up I try and switch to something with a real keyboard.
Doug fisher wrote on December 9, 2020 - 5:22pm
Where can I get the solar panels and other components to do this?
Grace Vance wrote on January 29, 2021 - 8:31am
I have to park 2013 Prius for over 1 mo storage. So very interested in maiming battery charge.
J wrote on February 22, 2021 - 6:50am
For long term storage disconnect the 12V battery from the truck. No need for this trickle charge b.s. Unless you are planning to turn your Prius into an RV like someone wrote here or like myself you do not need it.
Chuck wrote on August 28, 2021 - 12:27pm
Thank god. Someone that finely understands from the real side of things and how they actually work. I've 80 and been working on cars all my life, also aviation and 99.9% of what i see online is bull shit.
Alan Clarke wrote on July 17, 2019 - 8:30pm
I don't believe "... Absorbed Glass Mat or AGM batteries are in all years of Toyota Prius ..." - is correct for Gen 4 PRIUS either (ie since late 2015). Gen 4, like PRIME has the 12v battery under the bonnet (hood).
alain wrote on April 17, 2022 - 10:05pm
bingo - I've see Gen 4 pictures and the battery is under the hood and hopefully a normal terminal and acid one at 1/3rd the cost. No vent problem there anyway... bad design on Toyota - reminds me on BMW and their super expensive monster AGM battery in the trunk. common...
BRIAN wrote on July 18, 2019 - 7:40am
I have had the Optima Yellow Top in my 2007 since 2012 when the factory one died. I have only had one failure to start because the car was left on but not ready overnight. I do a full maintenance charge at the start of each winter. So OEM lasted 4 years Optima is 7 years old and still going strong.
Thomas wrote on December 13, 2019 - 9:24am
My yellow top optima has nearly lasted 4 years. I had higher hopes for it.
EDD wrote on December 15, 2019 - 12:16am
12/2019. Best auxiliary 12v battery for prius v owners is Duracell. Direct fit, vented, US manufactured. Available at Batteries+Bulbs, typically on sale. Free installation, immediate core charge refund, FOUR YEAR full replacement warranty (no pro-rated junk). Cheaper than dealerships.
PEmm wrote on December 27, 2019 - 7:49am
What’s the model number of this 12V Duracell AGM?
Kevin Baker wrote on June 3, 2022 - 1:55am
Its the one i got. Great battery, doublr vented, made in usa, think model is slu11?
PEmm wrote on December 27, 2019 - 7:50am
What’s the model number of this 12V Duracell AGM?
Deborah Routhier wrote on January 31, 2020 - 11:18pm
I have a 06 prius the dash worked sometimes and sometimes not. The red triangle light came on and the car continued for few minutes then battery light went into red and the car coasted to a stop and would not start. Towed it 50 miles home. I bought a new battery at o'Reilly but am reluctant to even try to hook it up because they said no return or refund if the problem turns out to not be the 12v. I paid 235 dollars for this battery. The car has 300k miles. Idk what to do. Dealership wants 160 dollars just to take a look or install a battery but what if it's not the 12v?
Gary wrote on February 23, 2020 - 5:56pm
Dont ge fooled by batteries + bulbs warranty. I bought a Duracell battery for my snowmobile. I wouldn't start it the next tear I brought it in and they said it was still good but it only had 11v they said they dont replace it under warranty unless it's under 10v I believe.
David Martel wrote on May 18, 2020 - 12:08am
2013 Prius Plug -in, 156,000 on the original Toyota battery. Eight years. Now showing me 70% charge and will not stay at 100% when using my Schumacher 12v charger. California car if that matters. Regular use. My experience with two Optima Batteries in two other vehicles was awful. I will never buy another one, period.
Jim Koralewski wrote on February 14, 2021 - 11:19pm
Never buy the current Optima batteries. They weren't bad when they use to be made in the U.S. Now, they are all made in Mexica and their quality and reliability has been terrible.
Bob B wrote on December 15, 2019 - 9:40am
We bought our 2010 Prius new back in the summer of 2010. It still has the original battery, and over 150,000 miles. I’ve been very happy with the performance of the original battery, but with another winter coming I’m looking at being proactive and replacing the 12 V battery. This article was very helpful.
Dave wrote on January 10, 2020 - 2:43pm
We also bought our 2010 Prius new in August of 2009 (Cash for Clunkers era). Ours also has the original 12v battery. The car is about to turn 110000 miles. Twice since owning it, it wouldn't start, but both times one of the two interior front dome lights were accidentally left on. I connected a 15 amp charger for a few hours before leaving home on those days.
Thomas wrote on December 17, 2019 - 1:04pm
Actually, I was just changing out our yellow top Optima and found it in a block of ice. The Prius had a defect which allows water leaks into the rear compartment and I hadn't noticed it until now. Between that and my short trips I'm sure killed the Optima much faster than it should have lived.
David Martel wrote on May 18, 2020 - 12:11am
I have used Optima's twice, two different cars, both failed with a few months and I returned them for a full refund. imho Over rated, hit and miss batteries.
jifbo wrote on May 27, 2020 - 3:36pm
Optima yellow top JUNK battery lasted less than a year. Absolute overpriced garbage and I won't their products again. People stick with stock options because they work better than most others. The solar storage batteries idea sounds interesting, but unless they really cost 1/2 of stock I wouldn't bother. If I did, I would buy 2, so I have a backup the NEXT time my unreliable Prius leaves me with no way home. Oh, and you want a real pain of a job? Just try replacing that 12v once you have no power and can't even get the hatch to open. Total design flaw. This Prius has left me totally stranded 4 times now, twice due to 12v battery and twice due to hybrid battery. Super pricey each time. Prius' fail fast and hard. No way to limp one along safely either. I was a diesel mechanic for 25 years and the unreliability of the Prius electrical is unacceptable. Now, in the age of social distancing, the very last thing I want is to get stranded when the Prius dies without warning, then have to sit in a random tow truck for who knows how long, less than 3 feet away from some random soul who makes their living interacting with other random souls all day long.. This 'planned obsolescence' is potentially lethal now. Thanks for nothing Toyota. Definitely not what I am looking for in terms of vehicle reliability... I will buy another hybrid, but not another Prius.
Twwhilei wrote on July 13, 2020 - 6:35pm
Use a charged portable jumper, still a pain, but after you attach your clamps properly attached, all your accessorirs will work again: hatch, etc.
Allyn wrote on August 9, 2020 - 5:17pm
Open the back hatch from the inside by flipping up the panel under the carpet, reach a finger inside the little access hole, and flip the little lever while pushing up on the hatch.
Nicholas D Haines wrote on November 18, 2020 - 9:25pm
I maintain 10 Gen 2 prii, great cars, just a psa EVERYONE, a cheap lithium booster pack is more than enough to run the computers if your battery went flat. And you simply pop the hood, open the relay box (driver side) and there is a positive terminal under a cover. Use this and any grounding point (bolt) to jump the prius. No opening the trunk required. DO NOT jump other cars from the prius as the terminal line is fairly low gauge and it would be very easy to damage the prius 12v system in this manner. I kinda hate that I come to a forum looking for actual research on an inexpensive alternative 12v battery just to read "buy the dealer battery scrubs". As if I didn't know how to buy a $200 agm battery

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