Experiencing a dead Car Battery is almost a universal rite of passage for vehicle owners. One day, your car starts perfectly, and the next, it greets you with nothing more than a disheartening click. While a jump start can often provide temporary relief, what do you do when your battery is stubbornly lifeless, refusing to hold a charge even after hours on a charger? It might sound too good to be true, but a relatively inexpensive tool exists that claims to bring car batteries back from the brink. These devices, known as battery desulfators, are touted as a way to reverse battery death. Skeptical but intrigued, we put one of these desulfators to the test, and the results were genuinely surprising.
Last month, we shared the tale of a trusty, compact 12V car battery, originally from a Toyota Prius, that finally gave up the ghost in our 2008 Smart Fortwo. This little battery had lived a full life, first enduring the high mileage demands of a Prius before being repurposed as a robust tool battery. It had jumped countless vehicles and powered numerous projects.
Alt text: Video thumbnail showing a person working on a car battery in a vehicle engine bay, emphasizing car battery maintenance and repair.
Recently, this Prius battery was being used to address the Smart car’s notoriously small battery compartment. The experiment was progressing smoothly until a recent cold spell seemed to deliver the final blow. Initially resigned to replacing the battery, encouragement from fellow auto enthusiasts and readers prompted a challenge: could this seemingly dead battery be resurrected? We took on that challenge and successfully revived not only the Prius battery but also another car battery that had been dormant for over a year.
Understanding Car Battery Death: The Role of Sulfation
In the past, we explored various automotive tools, highlighting their potential benefits for car maintenance and repair. Now, with a growing collection of project cars and a tendency to push their limits, we’ve become more hands-on with these tools. From using advanced diagnostic scanners to troubleshoot complex car issues, to employing borescopes for internal engine inspections, and experimenting with diverse electrical connectors, we’re now diving into the practical world of battery desulfation. Let’s understand why a desulfator might be necessary for your car battery in the first place.
Car batteries, specifically lead-acid car batteries, generate electricity through a fascinating chemical process. Inside, you’ll find lead alloy plates submerged in sulfuric acid, which acts as an electrolyte. These lead plates function as the anode and cathode. RS Components Ltd., a reputable battery supplier, provides a clear explanation of this process:
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.
This chemical dance reveals a critical point: lead-acid car batteries are not designed to be deeply discharged. This contrasts with lithium batteries, which have their own sensitivities, primarily to overcharging.
The textbook Batteries In A Portable World highlights that car batteries in high-discharge applications, such as golf carts, often have shorter lifespans. While these deep-cycle batteries are built with thicker plates and higher capacity to withstand frequent charge cycles, they still endure significant stress.
Sulfation is a major factor in car battery degradation. According to the same 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.
Battery Revival: Putting Desulfation to the Test
When faced with a dead car battery, common solutions include jump-starting your car or taking the battery to an auto parts store for a charge. Sometimes, luck is on your side, and the battery springs back to life. However, as we experienced with our Prius battery, sometimes a standard charge is insufficient, providing only a minimal voltage increase. Past attempts to force a charge have even resulted in overheating and damaging batteries.
After the Prius battery failed to respond to conventional charging, the desulfation challenge was presented. Devices designed to deliver the “overcharge” described in battery literature are available. These car battery chargers with repair functions work by sending pulsed charges to the battery. This pulsing action, applied over a prolonged period (ideally a day or more), is intended to break down and dissolve the crystalline sulfate buildup, thereby restoring battery function and capacity.
Desulfators are available as standalone units or integrated into battery chargers. Opting for a budget-friendly approach, we selected a 10-Amp car battery charger from Yonhan with a repair mode, priced at $26.99 on Amazon, based on user reviews suggesting its effectiveness in battery restoration.
First, we targeted the Prius battery, which showed a mere 2.89 volts after a day on a regular charger. Upon connecting it to the Yonhan charger, it almost immediately indicated a “full” charge within just ten minutes. Switching the charger to “repair” mode initiated the desulfation process.
In repair mode, the Yonhan charger displayed “PUL,” signaling pulsed charging. Real-time voltage monitoring revealed spikes as high as 16 volts for brief moments, before dropping back to around 12 volts, repeating this cycle continuously for 24 hours.
Surprisingly, the charger initially indicated an 80% charge, which then decreased to 20% after four hours in repair mode. Over the next day, the capacity reading gradually increased. As per the manufacturer’s warning, we periodically checked the battery temperature, which remained warm but never excessively hot.
After a full day of desulfation, the Prius car battery reached a stable charge of 12.8 volts – a remarkable recovery! But the experiment didn’t stop there. Next, we tested an even more challenging case: a completely dead Everstart car battery.
As Batteries In A Portable World points out, the longer a car battery remains discharged, the lower the chances of successful revival. This Everstart battery, dating back to March 2021, had been left in a project Smart car and died in late 2023, meaning it had been completely dead for at least a year. Its state was so dire it was even being used as a bed frame support.
This was the same OEM-sized car battery that prompted the search for a smaller replacement for the Smart car. Its snug fit highlighted the space constraints.
Could this deeply discharged car battery be brought back to life? After resolving the bed frame issue, the Everstart battery was connected to the Yonhan charger. Initially, a multimeter reading showed a flat 0.0 volts. The battery was so dead that the charger couldn’t even recognize it. To circumvent this, a jump pack was temporarily connected in series to “trick” the Yonhan charger. Again, the charger quickly registered a “full” charge within minutes, despite the battery’s true state.
Switching to repair mode, the Yonhan charger began the desulfation process on the Everstart. This battery required approximately two days to reach the charge level of the Prius battery. Over the following week, both batteries were rotated on the Yonhan charger, and gradually, both showed increasing charge levels and capacity readings.
It’s crucial to note that car batteries can release hazardous gases, as cautioned by desulfator manufacturers. Therefore, desulfation should be performed in a well-ventilated area, away from children and pets. During testing, batteries were placed outdoors during charging and brought inside only for monitoring.
After a week of desulfation, both car batteries were removed from the charger and left to rest for a weekend. By Monday morning, the Prius battery measured 12.7 volts, and the Everstart registered 12.6 volts. The Everstart’s recovery was particularly impressive, considering conventional chargers had failed to make any noticeable difference. The term “Neverstart” batteries seemed almost ironic in this context.
Of course, voltage alone doesn’t guarantee functionality. The real test was performance. The Everstart battery was installed back into the Smart car, and despite a cold morning, it cranked the engine to life just like a new battery. The Prius battery, connected via jumper cables, also started the car without any issue.
The Catch: Desulfation is Not a Miracle Cure
Does this mean these car batteries are fully restored to their original condition? Realistically, no.
As Batteries In A Portable World explains, permanent damage from sulfation occurs, especially in deeply discharged batteries like the Everstart. The extent of damage varies. Desulfators are not magic wands that create brand-new car batteries. Both tested batteries were already four years old and had experienced considerable wear and tear.
However, a desulfator can significantly improve a car battery’s condition, preventing it from becoming just a heavy, acid-filled brick. While these restored batteries may not perform like new, they can be functional for extended use, especially when supplemented with a solar trickle charger for maintenance.
MotorTrend tested a battery desulfator for two weeks, achieving a 13.1-volt charge, and the battery continued to perform for months afterward. Our batteries are currently working well, and further desulfation cycles may yield even better results.
For those considering battery restoration, investing in a higher-quality charger than the budget-friendly Yonhan model might be worthwhile (perhaps this NOCO Genius10). While the Yonhan charger proved functional, its build quality is undeniably basic. Its low cost might justify its use, but caution is advised.
Ultimately, if reliable car operation is paramount, replacing a dead car battery with a new one is the safest approach. A desulfated battery is still a repaired battery and may not offer the same long-term reliability as a new unit. However, for those inclined to experiment and potentially extend the life of a dead car battery, a desulfator, even an inexpensive one, demonstrates the validity of the concept. So, the next time your car battery dies, consider exploring the possibility of revival before discarding it – you might be surprised by the results!
