Hybrid battery repair is something that’s held interest for me since the early 2000s. When Toyota introduced the Gen 1 Prius in 2001, Berkeley streets were flooded with them. A lot of our customers purchased gen 1 Priuses, and once we proved we were pretty good at fixing them, we gained many more new Prius customers.
Back then it was my hope that one day I would be repairing and rebuilding Hybrid battery packs. As it turned out, replacing cells and reconditioning just aren’t viable options, much to my dismay. I love fixing things. Replacing things isn’t anywhere near as satisfying.
Can Hybrid Batteries Be Repaired?
Hybrid batteries can be repaired, but it won’t be a lasting repair. There are several issues that make hybrid battery repair challenging, but they can be overcome. There’s an issue with value vs. cost. And most importantly, there’s a huge issue with battery repair longevity after repair.
What Makes Hybrid Battery Repair Challenging?
First, a little background. “High voltage” batteries are made up of low voltage batteries connected in series. Each battery is connected positive to negative. When batteries are connected in series, the total pack voltage is equal to the sum of the individual low voltage batteries added together.
State of Charge
Once connected together, the state of charge of the individual low voltage batteries cannot be altered separately from all of the batteries in the pack. Once connected, the pack can only be charged and discharged as a unit.
Why does this matter? Well let’s imagine building a battery pack. What would happen if some of the low voltage batteries were fully charged and some were completely discharged when we assembled the pack? If we tried to charge the pack, the fully charged batteries would overcharge and overheat. If we tried to discharge the pack, the discharged batteries would over discharge and be damaged. This is one of the challenges. All of the batteries in the pack must have an exactly equal state of charge, but this is doable.
Battery Capacity
Another challenge is battery capacity. Each battery in the pack must have the same capacity. Batteries over time lose capacity. You’ll know this from your experience with phones and laptops. When new, the battery might last two days. After 3 years you may need to charge multiple times per day.
The battery capacity issue is very similar to the battery state of charge issue. A battery with lower capacity than others in the pack will fill quicker. Likewise it will discharge quicker. This will cause it to overcharge and over-discharge once its linked to the pack. You can’t simply buy a new battery and add it to an existing pack. (And manufacturers don’t sell new individual batteries for exactly this reason)
So, if you had a hybrid battery where one of the low voltage batteries had failed, you’d need to find a used battery that matched the capacity of the other batteries in the pack exactly. This issue can be overcome by testing and matching the capacity of all of the batteries you intend to assemble into a pack.
Cell Shorting: The Most Common Cause Of Hybrid Battery Failure
Here’s the real reason you can’t, or rather shouldn’t, repair a hybrid battery pack. Hybrid battery packs fail when a cell in one of the low voltage batteries shorts. This failure is impossible to predict. There are no diagnostic tests that will reveal that a cell is close to failure. One day it’s fine, the next it’s dead.
You might think, “So? I’ll just test used batteries until I find one with matching capacity, match it to the packs state of charge and save thousands”. And you wouldn’t be alone. Thousands of businesses tried the same thing, from a local upholstery shop, to wrecking yards, to manufacturing giants like Dorman, all with varying degrees of technical expertise and equipment. They all share one thing in common: failure.
What is the Life Expectancy of a Hybrid Battery
Here’s the thing about cell shorting. It seems to be mostly an age related fault. The car’s mileage isn’t a good predictor. A cell might short at 50,000 miles or 300,000 miles, but age is a pretty effective predictor. The NiMH batteries in the first three generations of Prius usually last between 12 and 15 years. There are outliers, but most fail within that window.
So, when you go to the trouble of repairing your hybrid battery, it’s pretty likely that on of the other batteries in the pack will fail shortly after. You’ll end up playing whack-a-mole until you give up and buy a new pack.
Battery Leakage
The other issue is electrolyte leakage. You know how your 12V battery terminals start to get crusty when the battery gets older and require constant cleaning? The same thing happens with hybrid batteries. This creates a host of issues. One is corrosion which will eat through wiring on the battery. The other is loss of isolation, which is beyond the scope of this article, but here’s a link to an article I wrote for ToyotaTech on the subject.
Dorman Remanufactured Hybrid Batteries
Are Dorman hybrid batteries any good? Well, they’re probably the best reman battery you could possibly buy, but they’re not good at all. Why? For the reasons I outline above.
I had a conversation with the lead engineer for Doman battery reman program at Sema one year. Super nice guy. Very knowledgeable. He explained their remanufacturing setup which sounded amazing. Automated capacity testing and sorting. I doubt anybody else in the game has the level of equipment and expertise.
When we started talking one of the first things he said was, “You’ve probably had some issues with our product, but we’ve been working on it and it’s getting much better”. There main issue at the time was electrolyte leakage from the terminals and the threaded insert in the bottom of the batteries used to connect the battery to the case. They had found methods to address both issues. The topic he avoided was age related cell shorting, and I don’t think there’s any way to correct that issue short of using new batteries.
How Much Does It Cost to Fix a hybrid Battery?
If someone held a gun to my head and said I had to get a reman battery, I’d buy a Dorman. But how much less would it be than buying a new battery from Toyota? On Amazon, the Dorman part number 587-001 is $1644 with shipping. A new Toyota battery part number G9510-47033 is $1950.
You save only $306. And if you check the reviews, you’ll find 50% of them are negative citing failures within two year of purchase. If you buy a new Toyota battery, it’s going to last as long as the original, and that will probably be the rest of the car’s life.
Here’s an article about new hybrid battery replacement cost.
Is Hybrid Battery Reconditioning a Real Thing?
Is it worth it to recondition a hybrid battery? What is reconditioning? Will if repair a failed battery?
Battery reconditioning is a real thing, which doesn’t necessarily mean you should be doing it, but it is real and will probably offer some benefit. The best reconditioning system was developed by Dr. Mark Quarto. He was one of the engineers on the GM EV1 project, the “Who Killed The Electric Car” car. Super smart guy. He knows far more about hybrids and EVs than I ever will. If you’re in this field and have an opportunity to take one of his classes, do it.
Now, back to reconditioning. Here’s the idea. As I mentioned earlier, when a pack is connected in series, all the low voltage batteries are charged and discharged together. Over time the batteries can get out of “balance” and their state of charge can drift apart. Mark’s machine requires removing the bus bar and connecting leads to the positive and negative cable of each individual battery. The device then does capacity testing, balances the pack, and maybe some other secret sauce stuff as well. It has been at least 10 years since I last talked to him about it.
These devices are sold to auto repair shops, or at least used to be, and there is also a franchise business called The Hybrid Shop that offers (or offered) this service at many locations. Their website seems to be broken, so they may not exist anymore.
Now, should you do it? Probably not. I recall the pricing being quite high. While the process may offer some benefit, I think the cost is disproportionate to the value.
Can Hybrid Batteries be Serviced?
Is there any preventative maintenance you can do to make your hybrid battery last longer? Well, there’s no way to top up the electrolyte or anything like that. The car’s battery management system will do it’s best to keep the battery healthy automatically. The one thing you can do if your battery is air cooled (most hybrids are) is to keep in cooling inlet vent filter clean (if it has one). On hot days use the A/C to keep the cabin at a reasonable temperature. If you have warning lights, have them checked. Finally, drive your hybrid regularly. That’s about all you can do. There is no other battery service needed.
Can You Still Drive if a Hybrid Battery Fails?
As I mentioned earlier, the most common type of failure is a shorted cell. When a cell shorts in an individual battery, the entire pack is brought down to the level of the battery with the shorted cell. This may cause several issues for Toyota hybrids, but the car can still be driven.
Here’s what you’ll likely notice. The battery cooling fan running all the time. Low power. The engine running all the time and revving higher than normal when driving. A dramatic drop in fuel economy. And finally, very low power when driving in reverse or a long delay before being able the back up. You may also struggle with hills, especially if you need to back up a hill.
So in short, yes you can drive with a bad hybrid battery most of the time, but you’ll probably want to get the battery fixed.
Can I replace a Hybrid Battery Myself?
You’re probably expecting me to talk about the dangers of high voltage and tell you to leave it to the professionals. I’m not gonna do it. Can you replace your hybrid battery? Maybe. You probably know better than me. Get a 3 day subscription to Toyota’s technical information website. Read the instructions. Watch some YouTube videos. (Remember that not everyone on YouTube is qualified, although many are.)
If replacing the hybrid battery seems like something you can do, go for it. It should be because you like doing projects though. The first time doing anything will take a while. Allow for mistakes and learning. Also, most shops won’t be interested in taking in a basket case, so if you commit, commit.
How to Start a Hybrid Car With A Dead Battery
This is really two questions. Hybrids have at least two batteries, a 12 volt auxiliary battery and a high voltage traction battery. If the 12V battery is dead, you’ll just need to jump start the car or recharge the battery. Check out this article on how to jump start a Prius.
Now, if the high voltage battery is discharged, you’ll probably need some expert help. We have a custom high voltage charger for just such occasions. Here’s an article about charging high voltage hybrid batteries I wrote for Import Service magazine if you’re interested.
Are Hybrid Batteries Recycled?
Frequently when I tell people what I do, they’ll start in about how all the battery packs are toxic waste and it’s going to pile up and ruin the planet. This simply isn’t true.
NiMH batteries contain Lanthanum, Cerium, Neodymium, and Praseodymium. Originally I assumed that this is what would make batteries worth recycling, but apparently I was wrong. It appears that the nickel found in hybrid batteries is where most of the value lies. If you’re interested in learning more, here’s a link to Cinco, a company that recycles all types of batteries, including hybrid batteries.
The core charge for a Toyota battery is $2000, which exceeds the cost of the new battery. Toyota is making sure that their batteries are recycled by making sure the old battery is returned to them.