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.

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.

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'.

Conclusion
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.

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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.