Pretty much everyone will experience a dead car battery at least once in life. A battery that fails to crank your car one day is just one of those unavoidable eventualities, like taxes or a visit to a toilet after consuming Taco Bell. But what happens if the battery you have on hand is super dead? I’m talking about a battery you’ve put on a charger for days and it still doesn’t work. There’s a cheap tool out there that can bring batteries back from the dead. It sounds like snake oil, but I just tested one and I’m blown away.
Last month, I wrote about how the slim Toyota Prius 12V battery that was in my 2008 Smart Fortwo finally bought the farm. This battery has been a little trooper. It first lived in my wife’s Prius, where it was subjected to 40,000 miles per year of driving. Then, once it displayed signs of age, I yanked it out and decided to use it as a giant tool battery. This battery’s done a bit of everything from helping me jump-start big trucks to powering my beaters when I need to move them back home to sell them.
Lately, I’ve been experimenting with using the battery as a solution to the Smart’s problem of having a battery compartment that’s just too darn small. The experiment went well, aside from the fact that the battery gave up on life after a recent cold snap. I originally decided to give up on the battery, but the wonderful Stephen Walter Gossin and a number of readers challenged me to bring it back. I did just that, then I brought back another battery that’s been dead for over a year.
How Batteries Die
Back when I wrote for the German Lighting Site, I used to have a series called Cool Tool, where I highlighted awesome automotive tools that you might not know about. At the time I didn’t really have the resources or need to test the tools I wrote about, so the series relied on the reviews of others.
I’m delighted to say that my addiction to collecting bad cars and then my poor stewardship of some of them have driven me toward using the tools I used to write about. I’ve used a technician-level diagnostic scanner to help me find issues in a variety of cars, a borescope camera has been helpful in bringing old vehicles back to life, I’ve experimented with different electrical connectors, and now I finally get to see how a battery desulfator works with my own two eyes.
Let’s start with why you would need a desulfator in the first place. Batteries generate electricity through a chemical reaction. Your typical lead acid battery is filled with lead alloy plates and sulphuric acid, which acts as an electrolyte. The lead plates act as the anode and cathode. RS Components Ltd., a battery supplier, explains what happens:
The lead plates act as an anode and cathode, while the sulphuric acid is an electrolyte that contains hydrogen and sulphate ions. Negatively-charged sulphate and positively-charged hydrogen are attracted to the lead cathode and anode respectively. When the appliance or device attached to the battery is turned on, a reaction occurs on the cathode as sulphate ions give up their negative ions and lead sulphate is created. As levels of lead sulphate increase, the electrolyte becomes weaker and resistance on the plates increases. This triggers the flow of negative electrons into the attached device or appliance.
As these electrons flow back into the battery’s cathode, a chemical reaction occurs between hydrogen in the battery and the lead dioxide in this plate. This produces water, meaning hydrogen ions are continuously supplied alongside the sulphate acid inside the battery, enabling the process to restart repeatedly.
In each type of lead acid battery, this reaction will work slightly differently to make it more appropriate to the particular use case its best suited for.
As you can probably guess from this explanation, lead acid batteries are not fond of being discharged. This is technically the inverse of the chemistry involved in lithium batteries, which don’t particularly enjoy being charged too high.
The chemical reaction is why, as the Batteries In A Portable World textbook purports, batteries in golf carts and other high-discharge applications tend to have shorter lives than other lead acid batteries. These vehicles tend to have deep-cycle batteries, which have thicker plates, a higher capacity, and are designed for high-charge cycles. But they’re still put under tons of stress for a battery.
Sulfation is a pretty big deal for a battery, from the textbook:
What is sulfation? During use, small sulfate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulfate converts to a stable crystalline and deposits on the negative plates. This leads to the development of large crystals that reduce the battery’s active material, which is responsible for the performance.
There are two types of sulfation: reversible (or soft sulfation), and permanent (or hard sulfation). If a battery is serviced early, reversible sulfation can often be corrected by applying an overcharge to an already fully charged battery in the form of a regulated current of about 200mA. The battery terminal voltage is allowed to rise to between 2.50 and 2.66V/cell (15 and 16V on a 12V mono block) for about 24 hours. Increasing the battery temperature to 50–60°C (122–140°F) during the corrective service further helps in dissolving the crystals.
Permanent sulfation sets in when the battery has been in a low state-of-charge for weeks or months. At this stage, no form of restoration seems possible; however, the recovery yield is not fully understood. To everyone’s amazement, new lead acid batteries can often be fully restored after dwelling in a low-voltage condition for many weeks. Other factors may play a role.
Bringing A Battery Back
If you experience a dead battery, you can jump-start your car or take the battery to an auto parts store and have the battery put onto its charger. If you’re lucky, the battery will come back to life. If you’re unlucky, like I was with the Prius battery, the battery might get a charge of a few volts but that’s it. In the past, I made a battery boil by trying to bring it back with force.
I tried charging the Prius battery for hours and nothing worked. Each charge from my charger would either complete with the battery not actually making any progress or the charge would just fail. I was ready to give up and buy a new battery, but then Stephen Walter Gossin issued that challenge.
There are lots of devices that you can buy which are designed to provide the overcharge as described by the textbook passage above. In essence, these chargers work by sending overcharge pulses to the battery being restored. Doing these pulses over and over for at least a day is supposed to help break off and dissolve crystalline buildup, restoring function and capacity to the battery.
You can buy a desulfator on its own or you can get this feature as part of a battery charger. I’m a cheapskate, so I looked for the cheapest charger with a battery repair feature. The one I bought was a 10-Amp charger from Yonhan with a repair function. I paid $26.99 for the unit based on the reviews on Amazon that said the device successfully restored a battery.
First, I decided to restore the Prius battery. This battery had a standing voltage of 2.89 volts after sitting on another charger for about a day. I hooked it up to the Yonhan charger and it read a “full” charge after only 10 minutes. Then I hit the selector until the charger landed on the repair option.
When you activate the repair function on my specific unit, “PUL” shows up on the screen indicating that it’s ready to start shooting pulsing charges at the battery. When I measured the pulsing system in real-time, I watched as the voltage climbed as high as 16 volts, but only for a second before dropping back down to about 12 volts. The device did this over and over for an entire day.
To my surprise, the charger started off by claiming the battery was at 80 percent, but after about four hours on the repair setting the charge indicator now claimed a 20 percent charge. I let the charger eat at the battery for the rest of the day. Little by little, the capacity crept back up. Yonhan warned to frequently check the battery to make sure it wasn’t overheating. The battery got warm, but never too hot.
After a whole day on the desulfator setting, the Prius battery achieved a standing charge of 12.8 volts, which is great! We’ll return to the Prius battery in a moment. Next, we’ll see what happened with a more challenging battery. Check out the photo below where the charger wasn’t even seeing the super dead Everstart battery:
As the Batteries In A Portable World book notes, the longer a battery stays dead, the less of a chance you might have to bring it back from the dead. I decided to put that to the test, too.
I used to have a wall of batteries at home. These batteries used to sit on tenders to stay nice and topped up for when I needed them. Well, I got a bit sloppy, left some of these batteries in cars that were parked outside. They died and my regular Deltran battery chargers couldn’t bring them back.
One of those batteries was the pictured Everstart unit from March 2021. This battery died somewhere toward the end of 2023 after I left it in my project Smart for too long. In other words, it’s been dead for at least a year. This battery has been dead for so long that it has served as a structural component of my bed at home after a piece of my bed frame snapped.
This is the OEM-sized battery that motivated me to try to find a smaller one that works. See how tight it fits in there:
But I wondered: Could this battery be brought back? I finally got around to doing a proper fix on the bed frame and then put the Everstart on the charger, too. The Everstart was initially so dead that it read a fat 0.0 volts on my multimeter. It was so dead that my charger couldn’t even detect it. So, I first tricked the Yonhan charger by hooking up a jump pack in-line with the battery. Once again, the Yonhan claimed a full charge within ten minutes even though the battery was super dead.
Just like with the Prius battery I selected the repair function and then let the Yonhan eat. This battery took about two days to reach the level the Prius battery got to. Throughout the rest of the week, I began swapping the batteries on the Yonhan charger and little by little, both reported higher and higher charges with the charger claiming higher capacities.
Before I continue, I should note that batteries can release some toxic gases. The manufacturers of these desulfating devices warn of such in their booklets. Because of this, I would avoid using a desulfator indoors nearby pets and children. I put mine on the deck outside when I wasn’t bringing the batteries inside to check on them.
Finally, after a full week, I took both batteries off and then let them sit for a whole weekend. As of this morning, the Prius battery was reading about 12.7 volts while the Everstart was showing about 12.6 volts. I was blown away by this, especially with the Everstart. None of my other chargers were able to do much of anything with the Everstart. I was beginning to see why some enthusiasts call them Neverstart batteries.
Of course, voltage isn’t everything. How does it actually work as, you know, a battery? Well, I first dropped the Everstart into my Smart and even though it was a cold winter morning in the Midwest the Everstart cranked the Smart into life like it was a brand-new battery.
As for the Prius battery, I hooked that up to the Smart through jumper cables–the same process I use to move a car a very short distance–and it also had no problems starting up the car.
There’s A Catch
So, does that mean that my batteries are fully restored? Not even remotely.
As Batteries In A Portable World notes, batteries will get permanently damaged from sulfation, especially if they’ve been dead for a while like my Everstart. The extent of the damage will vary between each battery and each situation. As awesome as a desulfator is, this device isn’t giving you a brand-new battery. Both of my test batteries are still four years old and both of them have been abused for far longer than they were designed for.
However, the desulfator should at least bring your battery back enough that it’s no longer a lead and acid brick holding up your bed. I have no doubt that both of these batteries aren’t nearly as great as they used to be. But hey, so long as I can keep that Everstart alive using a solar trickle charger that’ll be good enough for me.
The car fiends over at MotorTrend put a battery on a desulfator for two whole weeks and theirs got back to a charge of 13.1 volts. Their battery kept on going for months after the restoration was complete. Mine is working fine for now, but I’m going to put my batteries back onto the desulfator to see how much further I can restore them.
My advice? If you want to restore batteries, buy a charger that’s better than the one I have (maybe this one). While the Yonhan seems to do the job, it’s ridiculously cheap. The build quality makes a McDonald’s Happy Meal toy seem top-shelf. It’s so cheap that I make it run outside in case something goes wrong. Am I being a bit much? Maybe, but the build quality is that bad.
At the same time, if you absolutely need your battery to work, I’d also just buy a new one. A restored battery is still a damaged battery and it can still let you down when you need it the most. However, the little $27 charger taught me that the concept is sound. If you’re about as silly as I am, the next time your battery dies, don’t throw it into the proverbial ocean, try bringing it back from the dead!
(Images: Author, this post does contain an Amazon affiliate link, and if you click it and buy something we might get a commission – MH)
There is some magic that is possible and it’s a lot easier if the battery is maintained. I’m thinking my Honda Motorcycle battery an 11 year old Yuasa AGM that has outlived a couple of regulator/rectifiers so far on the 25 year old bike. It sees 8 months of the year of just grab and go (one of 2 bikes) and 4 months continuously on a CTEK 0.8Amp maintenance charger with a recovery mode.
I’m sure I could wander out to the shed right now and it would show ready to go.
My Kawasaki is similarly maintained, but the battery is relatively recent.
My poor Ford Fiesta, it’s a back up vehicle and I do feel bad for the gaps in use that it sees. The original battery lasted 6 years, this one is four and I’m expecting the day I wish I’d plugged it in. It’s a fun car and I’m feeling guilty after reading the article, it may get a maintainer/recoverer yet.
I have a NOCO Genius with a desulfator function and while it has successfully brought back old batteries to good voltages, the batteries will lose charge very quickly if left hooked to a car and after just a few days, the car won’t start. In my experience these desulfators can restore voltage but can’t restore capacity to an useful level.
I’ve since stopped bothering and I just replace an old, dying battery.
I had a (N)everstart that came from a Ford Taurus that I put in my jeep TJ ,it lasted 13 years then shorted out at the end of our driveway .Had to walk up the hill ,get the tractor and tow it back up the driveway.
The Kubota (diesel) tractor battery is now 11 years old ,I have always used my Snapon smart charger a few times a year on it just to keep it topped off even though it gets used hours at a time .That seems to really help longevity of a battery.
Ive had the lucky fortune of having a buddy who works for a battery testing company and weve had a few duds that we asked if he could go all dr Frankenstein on them.
They can come back when you cram a couple hundred volts into in quick bursts, but also helps theyre held in a testing chamber.
But do know this, if you have an AGM style or glass matt, youre really cornholed if its dead, as those cant be brought back.
The hydrogen sulfide gas is always a great time when they go kaboom with sparks when discharging, ask how i know.
Thank you for bringing the truth about AGM. I work for an industrial battery company and have learned this many times over. At least flooded batteries have some resilience and in stationary applications free from heat or shock they can go on 20 years or more. AGM is lucky to get five years in absolutely ideal conditions. There are some exceptions to this but none that you’ll see in the car world.
Ive had some dumb luck with yellow tops, but otherwise theyre kind of a random lottery if they drop a cell or not.
We too have had some lead acid we thought no way itl.come back, and with brute force charging we’ll get em to bout 40 or 50 percent capacity and they last a lil while.
We had a hyundai that lasted 11 years on the factory battery, and only replaced it because it was testing slightly weak, hard to say how long that bad boy woulda keep chugging.
The AGM battery in my truck went 10 years and never failed to start, even in Minnesota winters. I find this claim to be more than a little dubious. Maybe in your particular industrial use case that’s true, but not necessarily in automotive.
In my experience, a properly maintained AGM has no problem reaching 10 years of service life.
One important bit: Make damned sure your battery is topped off with distilled or deionized water ( if applicable) BEFORE you even think of hooking up a charger or a desulfonator. Low water may have been what killed it in the first pace.
I’m glad you were able to at least partly recover the battery. If its not powerful enough for a car it might be a good candidate for a UPS.
The. next installment must be the autopsy by chainsaw for entail examination.
My 2005 MDX sits for weeks/months at a time and my desulferator is a lifesaver. The car is outdoors, so a battery tender is really not a great option. If I watch it and maintain it, the AGM battery will last a long time. I do suspect a parasitic drain I have not found – likely just ‘modern’ stuff.
If don’t drive it for a while “try” to remember to put it on the desulferator/trickle charger overnight. Seems to help if I don’t let go dead.
Maybe a solar charger would help keep it juiced?
I’m a serial battery killer by unintentionally letting some of my cars go many months without driving and have one of the Noco genius 10 chargers with a battery repair function I seem to use about 2-3 times a year. They really do work, however my experience is that a battery can be revived 3 times max, and each time the self-discharge rate doubles. When the battery eventually does fail it fails hard without much warning so I wouldn’t use it for a daily that I depend on to get to work, however for project car type stuff this has probably saved me several times more than what it cost over the last 5 or so years.
Same – last bad battery in my MDX would die if I left the door open for 5 minutes. You had one shot at getting it to start. I kept it alive for longer than I should have.
Yup. I have the same NOCO Genius and while it can restore voltages, it can’t restore capacity so the “revived” battery won’t retain it’s charge long enough for it to be trusted.
If my old Craftsman charger ever fails I’ll consider this, but despite losing the ammeter needle my current unit is approaching 40 years old and still works
I have a charger from harbor freight that reconditions batteries, works mint – I just went and bought their cheapest digital that does reconditioning. Have resurrected 3 batteries now.
This seems like a better approach than a chainsaw
So I can buy a device that will squeeze a bit more juice out of a dead battery after a day or so? Leaving me a battery that has to stay on life support and will eventually die again? Most likely when it’s least convenient. I don’t get the use case. Sounds like a lot of work to avoid a couple hundred $ on something that will work great for years.
i used the desulfator functions on my girls’ “barbie jeep”. i brought them back from the dead a few times, and one of the batteries still works, but the jeep took a dump. Also, my old wrx battery is still alive and kicking after sitting on the garage floor for a few years. I don’t know at this point why i still keep it.
It is great for long term maintaining a marginal battery and can give more life to a bad one. It is not a cure all and I would not want to rely on it for a daily.
You answered your own question. “avoid a couple hundred $ on something”. If it isn’t a critical use case, i.e. daily driver, then why not?
David Tracy level shenanigans
A plastic box full of sulphuric acid supporting your bed in your bedroom doesn’t seem like the best idea.
My wife and I had a good laugh when the Chinese-made frame of our bed collapsed under circumstances that will go undescribed.
I’m pretty sure I had a volt/ohm meter that looked a lot like yours. I have a nicer one now, but seeing yours brought back a few memories.
Batteries and charging systems have vexed me for decades. My 2001 Jetta TDI had some kind of parasitic battery drain I was never able to track down. A week of sitting idle was about as much as it could handle before being unable to start the car. And an early 80s Suzuki GS 850 I had went through a couple of regulator/rectifier modules due to a weak battery.
My 2017 Honda’s OEM battery was done after three years in SE TX. I bought a battery at Walmart five years ago. I received a coupon for a $20 oil change from my now local Honda dealer in Washington that included a maintenance inspection, and they suggested I buy a battery from them, but after the OEM one died after three years, I declined. But the headlights do dim when I crank the steering wheel while parking and the electric PS system has to work hard, so I realize I’m getting close to replacement time.
My CTEK smart maintainer has an automatic pulse restoration mode built in, and I assume that it works pretty well. I’d have a hard time trusting a super-bargain-basement charger for long-term continuous use, lest it burn down my garage/house. FWIW CTEK makes the “factory accessory” battery maintainers sold by Porsche, Subaru, and no doubt a bunch of others.
I have nothing of value to add except the fact that I had that exact same 1:6th scale New Bright PT Cruiser when I was younger. That thing has to be 20 years old, where on earth did you find that??
A co-worker gave it to me about a decade ago!
I use cheap 12V lion packs for the lights on my custom bikes and I charge them outside or supervised near a window I could throw it out of in the worst case and I even do this with the good quality LiFPo for my e-kayak, so you won’t get any criticism from me. I’ve also seen a large deep cycle PBA on a Marine Travelift blow up, so to me, it’s a small amount of annoyance when charging to save from a potential really bad situation. That deep cycle went off like a 1/2 stick of dynamite and, even contained within the fuselage of the Travelift (though I believe the service door was open, it opens on the side, so there was a roof of sorts over the battery), most of the top managed to probably attain 80′ of altitude and spray acid over a pretty good spread. I had seen the marina owner’s kid near it maybe 30 seconds earlier and ran over expecting a bad scene. Didn’t see him, so then I thought he might have been blown into the water or under a boat or whatever, but luckily, he had gone down to another dock before it went off and was fine.
Speaking of tossing things out when they fail, it was way back when we were camping in the parking lot of Boreal Ski area in our slide-in camper. We were using a basic white gas lantern when it leaked and caught on fire. Dad opened the back door and tossed it out. Defenestration of failing flaming objects is the right thing to do.
I have an extinguisher, but I’d much rather run outside to deal with a fire in the driveway than fight it inside.
I thought the issue with gas generation was that it was explosive hydrogen, not that it was toxic?
So if I buy a Toyota Mirai, I can just fill the trunk with batteries on desulfinators and I’ll have a fuel source?
Might be cheaper than buying it on the black market too. 😉
Regular charge/discharge cycles can make hydrogen, but extremely high charge or discharge rates can cause the acid to evaporate and give off some less-than-ideal gasses.
Years back….(90s). I put my Miata in the garage for the winter. Spring left me with a dead battery. I don’t remember the details of my resuscitation of it. I do know the fancy electronic charger wouldn’t even try. I had to use the old style ” buzz box”. I think it involved several sessions of “jump ” mode. Then back to the smart charger. Anyway I got a few more years out of it. I think I did this on a few batteries,
A lot of microprocessor-controlled chargers will just give up on a deeply discharged battery. There’s nothing there for the circuit to sense. The solution is to hook up the charger and turn on a load, like parking lights. The charger should “wake up” and begin delivering a charge.
Of course, modern cars’ electronics may not like a stray charge running around, and battery chargers’ output can be a bit wonky as a power supply. Better to remove the battery and jumper a spare headlight across the battery terminals. (An old sealed beam unit works great for this!). Let it go with the load attached for a while, and then remove the load and try to get a proper charge cycle started. If the battery has taken any charge at all, it will probably work. Bonus points if it kicks your charger’s desulfation cycle into action (if it has one). Let it be and you may come back in the morning to a battery that’s actually charging properly.
Better “Trouper: a person who deals with and persists through difficulty or hardship without complaint.”
But now I have to buy another thing that I can’t store.
That neat I never saw that setting with a charger. My last dead battery I was too chicken shit to do anything with, it was swole up like Dwayne Johnson. I didn’t even want to try and jump it. I brought it down to AutoZone as soon as possible and exchanged with for a Duralast AGM.
Curious how old your Duralast AGM is?
Been using the Optimas for close to 20 years at least. I have never had to replace one, even after 14 years.
The Duralast AGM is only 4 months old at this point. Its the first time I’ve ever bought one, hoping it will go the distance. The swollen battery was an OEM VW/Audi battery.
Good luck with it.
I think you’re supposed to use a chainsaw on swollen batteries. Right?
/Don’t use a chainsaw on batteries.
Thankfully, it wasn’t close to chainsaw territory and managed to come out with no help
Once the battery is bulging I would not even think of trying this because you can have unintended contact paths between the plates in the battery.
This article reminded me to go hook up the $7 trickle charger I bought to the battery in my w126 that’s stored for the winter. Previous owner installed a red top and I’m keen to not pay for a replacement.
So, thanks Mercedes for reminding me to care for my Mercedes!
I tried something similar way back before chargers had safety shutoffs built-in. It’s the one and only time that I tried to over-charge as it exploded. I ran to the shower instantly 🙁
I’ve used a Schumacher BT-100 (https://www.schumacherelectric.com/products/battery-load-tester) battery tester in the past to try to get an idea about how many Cold Cranking Amps (CCAs) a battery has. This unit uses a resistor to simulate the load for 10 seconds.
I’ve had problems with “Smart” chargers on deep-cycle batteries. They would say the battery was dead, whereas a dumb charger would charge it fine and everything would be good.
The de-sulphating setting never did much for me, glad it worked for you
The Schumacher’s batteries have no charge?
I’ve found that microprocessor-controlled chargers need a “Deep Cycle” mode setting to properly handle deep cycle batteries. No setting, usually no luck with them.
Back from the dead? OMG ZOMBATTERIES! 🙂
That looks like a very useful tool concept; I was not aware they existed but will look for one. I’m currently using a basic 6V/12V charger – an upgrade several years ago that replaced an old-school Craftsman charger that has an analog needle in the display.
COTD!
Don’t count on that restored battery too much. I’ve done that before. It will help for a little while but once a battery has gone down that low, its done.
that is mentioned at the end.
I added the note at the very last second right after it was published (I realized I might have implied using this was would net you a reliable battery). Pat commented really quickly. 🙂