Gel battery repair. How To Recondition Your Battery

Recondition a Lead Acid Battery, Don’t Buy A New One

Lead acid batteries often die due to an accumulation of lead sulphate crystals on the plates inside the battery, fortunately, you can recondition your battery at home using inexpensive ingredients.

A battery is effectively a small chemical plant which stores energy in its plates. They are chemically charged with an electrolyte which is a mixture of distilled water and sulphuric acid. When the battery is discharged, the lead active material on the positive plates reacts with the sulphuric acid and produces lead sulphate. When the battery is charged, this process is reversed and the lead sulphate crystals react to form sulphuric acid again. The battery fails when there is an excess build up of lead sulphate crystals which then do not allow sulphuric acid to make contact with sections of the plate. These crystals harden and eventually cause a chemical imbalance in the electrolyte.

In most cases, hardened crystals can be removed using a solution of magnesium sulphate. This method doesn’t restore a battery back to original condition but it will restore it to around 70-80% of its original capacity and can be repeated, allowing you to get a few more years of use out of your battery without having to replace it.

What You Will Need To Recondition Your Battery

Take the battery out of the vehicle, motorbike or scooter and put it onto a solid work bench.

Some battery’s cells are clearly visible on top of the battery and are sealed with screw in caps. Others, like mine, are protected by a “sealing” strip. You may need to cut the edges of this strip to get it loose but it is almost always removable. Look for the edge of this strip and try to pry it up using a flat screw driver, if it is glued into place, try to cut around the edges of the strip using a sharp craft knife.

Once this has been removed, you will also need to take the caps off each of the individual cells in order to get to the battery acid. Some batteries have small rubber caps like these, others (typically on larger batteries) have screw in plugs which can be removed with a large screwdriver, they’re not usually very tight.

Using a syringe or dropper, carefully drain each cell one by one until they are all around 50-60% full, if some cells are already lower than this then exchange some acid from the fuller cells. You don’t want to take too much out as you will then struggle to charge the battery again. The liquid you are removing is a strong acid so put it into a glass container and be careful not to mess any of it on your hands or clothing.

Make sure that you dispose of the removed battery acid in a safe and responsible manner. The removed battery acid is extremely corrosive and contains heavy metals, mainly lead.

Now you need to make a saturated solution of Epsom salts (magnesium sulphate) and distilled water. Do this by boiling water and continuously stirring in more salts until no more will dissolve in the water. Then fill each cell with the Epsom salt solution to the full level line using the syringe or dropper.

When charging the battery while it is being reconditioned, some gas will be released, so it is advisable to leave the caps open. Connect a battery charger to the terminals and let it complete the charging cycle. If the battery is heavily drained or damaged, it may have to be charged overnight with a trickle charger at a very low amperage. If you do not have a battery charger then replace the battery cell caps and covers and reinstall the battery in the vehicle. Jump start it and then take it for a full hour or two drive to allow the battery to charge using the alternator.

The reconditioned battery should now last another 6 months to a year and can usually be restored using this method about three to five times until it is no longer effective.

Edit: As some users in the Комментарии и мнения владельцев section have suggested, the best solution would be to let the reconditioning process run for a few days to properly “clean” the plates and then drain the Epsom salt solution from the battery and replace it with the recommended 35/65 acid solution. Make sure that your battery is discharged before removing the Epsom salt solution and replacing it with the acid solution.

Have you tried to recondition a battery using this method or a similar method? Let us know in the Комментарии и мнения владельцев section below.

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Hi, my name is Michael and I started this blog in 2016 to share my DIY journey with you. I love tinkering with electronics, making, fixing, and building. I’m always looking for new projects and exciting DIY ideas. If you do too, grab a cup of coffee and settle in, I’m happy to have you here.

144 Комментарии и мнения владельцев

About 15-16 months ago I added distilled water to my cars completely dead battery. I happened to have a charger that loved to overcharge, causing the batteries electrolyte to boil. I continued to overcharge and top of the fluid (in a vented area, of course). This was a test to see if it would clean hardened lead sulfate from the internal plates to extend its life. The battery lasted till this winter before drastically losing its capacity. So I’d like to safely create my own solution of battery acid mixture – just like humanity did when lead acid batteries were serviceable in the early days. I don’t see that topic covered too often.

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What’s in a gel battery?

A gel battery is a dry battery since it doesn’t use a liquid electrolyte. In a gel battery, the electrolyte is frozen with silica gel. This keeps the electrolyte inside the battery, preventing it from evaporating or spilling.

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This design stabilizes the battery and gives it a low self-discharge. This is a handy feature for batteries that lie idle for long periods.

Are gel batteries better than flooded batteries?

A flooded lead acid battery is a wet battery since it uses a liquid electrolyte. Unlike a gel battery, a flooded lead acid battery needs maintenance by topping up the water in the battery every 1-3 months.

Gel batteries are the safer lead acid batteries because they release less hydrogen gas from their vent valves. This makes them safer to install where there is limited ventilation. Hydrogen release or gassing is a minor safety concern with flooded lead acid batteries.

Because of how they’re made, they can be oriented in any way. They can be stacked pancake-style which may improve cycle life. Flooded lead acid batteries are kept upright to avoid acid spills.

Gel batteries are, however, more expensive. Check out this guide if you’re curious about how flooded lead acid batteries work.

Are gel batteries better than AGM batteries?

Absorbent Glass Mat (AGM) batteries are the other sealed lead acid battery. How do gel batteries compare to AGM batteries?

For starters, gel batteries can be more expensive. They also need specific chargers to prevent overcharging. Not using these chargers reduces the batteries lifespan.

They’re also don’t work as well with appliances that need a higher current because they have a higher internal resistance.

On the other hand, gel batteries have a longer lifespan. This is because:

  • They hold more acid because of their design.
  • They have a better temperature tolerance. They have improved heat transfer to the outside. The gel moves heat, whereas the absorbent glass mat of the AGM acts as an insulator.
  • They also maintain their performance over a longer period. AGM batteries gradually fade as they get older.

Check out my guide to AGM batteries for more on absorbent glass mat batteries.

Deep-Cycle Lead-Acid Batteries for Solar

There are two main types of lead-acid batteries available, flooded lead-acid batteries and sealed lead-acid batteries. Both batteries use the same basic chemical principles to produce electricity. Each battery has a positive lead dioxide plate (cathode), a negatively charged lead plate (anode), and a mixture of sulfuric acid and water called an electrolyte.

When the plates are placed in the electrolyte mixture and connected to wires from a solar panel system, they can produce electricity. While both flooded and sealed deep-cycle batteries use lead plates and an electrolyte to produce a current, their designs differ significantly.

Flooded Lead-Acid Batteries

A flooded battery is the most basic design and, therefore, also the least expensive. Flooded lead-acid (FLA) batteries use rounded plates covered in electrolyte water mixed with acid. Because the plates need to be continually flooded (hence the name), these batteries require some regular maintenance. To keep up flooded lead-acid batteries, add distilled water once the battery’s evaporation levels are too high.

To add distilled water, you must be able to open the plastic casing around the batteries. This design means the batteries need always to be standing upright and be in a well-ventilated area. Without proper ventilation, the hydrogen gas that emits every time the batteries discharge could build up to dangerous levels.

Without proper maintenance, these batteries will have fewer life cycles. However, when cared for properly, they can last anywhere from five to eight years for home energy use.

Sealed Lead-Acid Batteries

As their name implies, sealed lead-acid (SLA) batteries don’t require topping off the water regularly so that they can remain permanently sealed. Instead of replenishing the water supply, SLA batteries have one of two ways to contain their liquid.

The first design is to include separators made from fiberglass between the positive and negative plates. The other design is to convert the liquid into a gel. With either method, the batteries will release hydrogen gas during discharges, so you’ll still need to keep them in a well-ventilated area, even if storing them on their sides is an option.

Absorbent Glass Mat (AGM) Batteries

When fiberglass is used to absorb the electrolyte and prevent it from leaking or evaporating, it’s called an absorbent glass mat (AGM) battery. The fiberglass acts sort of like a sponge and keeps the electrolyte close to the positive and negative plates. This allows AGM batteries to have a deep discharge while still providing the sulfate to mix back together with the hydrogen. This process is what lowers the amount of hydrogen gas released during discharges.

AGM batteries can discharge hundreds of times at up to 80% capacity and usually last around five years when used with a home energy system. While their low maintenance and easier storage make them appealing, they cost up to two times more than their counterparts as the design is more complex and requires more materials.

Learn more about What is an AGM Battery here. What is an AGM Battery

Gel Batteries

The other type of sealed lead-acid battery is a solar gel battery. AGM and gel batteries come with the same conveniences but operate differently. The silica gel in deep-cycle gel batteries suspends the sulfuric acid, giving the battery greater stability. It also has a lower rate of self-discharge over a long time.

In addition, gel batteries release the least amount of hydrogen gas when they discharge, meaning ventilation isn’t as much of a priority. Solar gel batteries also function better at higher temperatures than their competitors, making them wise for warmer climates. However, the gel can run into issues in colder climates, something to keep in mind if you plan on storing your batteries in a basement or garage during wintertime.

Because deep-cycle gel batteries can easily overcharge, you need to observe them rather closely to ensure a longer lifespan. It’s essential you connect these devices to the appropriate battery charger. A deep-cycle gel battery charger can monitor voltage and prevent it from going over the limit that solar gel batteries can handle. Without the proper gel cell battery charger, you may end up disappointed in your gel batteries’ performance.

AGM vs Gel Battery

From the introduction of the two types of sealed lead-acid batteries above, you can notice that AGM and gel battery are quite distinct with each other in many ways. Here are the details offering you more ideas how to distinguish the two batteries.

  • Working principle: the sealing principle of the two cells is the same. The difference lies in the way the electrolyte is fixed and the way that oxygen is supplied to the anode channel.
  • Interior structure: AGM batteries have an electrolyte (pure sulfuric acid) that is kept in suspension by the fiberglass, and come with thicker plates. Gel batteries use a gel electrolyte (made of sulfuric acid and silica gel) and thinner plates.
  • Discharge capacity: AGM batteries have a lower discharge capacity than today’s gel-sealed batteries
  • Internal resistance: gel batteries have a higher internal resistance than AGM batteries.
  • Thermal runaway: gel batteries appear to be more adaptable to high temperatures, while AGM batteries can easily suffer from poor thermal conductivity.
  • Lifespan: there are many factors that affect the service life of VRLA batteries, both in terms of battery design and manufacture, and in terms of user usage and maintenance conditions.

Are 12V Gel Batteries Good for Solar?

A 12V 100AH gel battery does have possible applications for solar energy. However, not all solar setups will work well with deep-cycle gel batteries. Because of the amount of energy these batteries produce, along with their cost, 12V solar gel batteries work best with off-grid solar energy systems, such as small solar panel kits designed for RVs, boats, tiny homes, vans, and small cabins.

If you plan on utilizing solar power to provide energy to your entire home, deep-cycle gel batteries may not be the best investment. With more extensive solar setups, lithium-ion batteries are likely a better choice.

Are Lead-Acid Batteries Better than Lithium-Ion Batteries?

The answer to this question really depends on your need and situation, but generally speaking, no, lead-acid batteries are not better than lithium-ion batteries. Lithium-ion batteries are the latest in rechargeable storage technology for solar, electric, and other forms of energy. Because they use newer, more advanced technology, they create several advantages over their older competitors.

For starters, lithium-ion batteries have a greater energy density, meaning they can store more energy using less space. Also, these batteries can be discharged regularly at up to 80% capacity without any downsides. Best of all, they have a greater tolerance for temperature fluctuations, making them more versatile and applicable to things like electric vehicles.

And to top it all off, lithium-ion batteries will last for at least ten years easily. Most lead-acid batteries will only last approximately seven years, and during that time, they won’t produce as many kilowatt-hours.

information can be found in another article, Are Lithium Batteries Worth the Investment?

Which Is Cheaper?

When looking solely at pricing, you really need to break things down more extensively than just comparing price tags. To purchase and install lead-acid batteries for a complete home solar energy system, you can expect to pay around 7,500. However, the price will vary depending on the system’s size and installation costs. It’s going to run closer to 12,000 on average to do the same with a top-of-the-line lithium-ion battery setup.

As long as it’s for storing solar energy from solar panels, both battery setups would qualify for the federal solar tax credit, saving you 26% in equipment and installation costs. That means that a lead-acid battery system could cost you closer to only 5,550, and a lithium-ion battery setup would be more like 8,800.

However, another factor you should consider when it comes to costs is each battery’s lifespan. If the average lead-acid battery setup lasts seven years, you’d be spending around 785 per year. Since lithium-ion batteries are reliable for at least ten years, that averages out to 880 per year, after the federal solar tax credit.

In the end, you have to decide if the higher price tag of lithium-ion batteries is worth the conveniences and advantages you would gain compared to lead-acid batteries. As lithium-ion batteries grow in popularity, their price points will likely go down, making them a worthy long-term investment.

Deciding on Deep-Cycle Gel Batteries

Solar gel batteries can be an excellent option for certain solar energy system setups that don’t require powering an entire residence or building. These batteries operate much like other lead-acid batteries but come with a few extra advantages.

Deep-cycle gel batteries release less hydrogen gas during discharges. Because of their interior gel design, you can store them in various ways without the risk of leaks or malfunctions. They also cope better with being kept in higher temperatures but still have heat limitations.

For these reasons, 12V solar gel batteries are ideal for smaller solar panel setups, such as for a tiny home, RV, small cabin, or boat. Even though gel batteries can be wired into larger battery banks, the sheer number of gel batteries you would need for a standard residential solar setup makes them ineffective for such purposes. Instead, you may want to consider absorbent glass mat batteries or lithium-ion batteries for your home solar system.

Regardless of what setup you settle on, going solar is always going to be a wise investment. As renewable energy becomes more prevalent and necessary, solar energy systems (no matter how big or small) will create opportunities to have power when other alternatives run out or aren’t available.

Each year solar energy becomes more and more affordable, making the switch to solar an obvious choice. It may involve doing a bit of research and learning about the differences between gel batteries and lithium-ion batteries. Still, we’re confident it will be worth your time and energy.

But if you want to avoid further hassle and select the right battery for your solar power system faster, Renogy offers you an all-in-one solution. Gel batteries. AGM batteries. lithium phosphorous batteries. and solar generators which also act as a role of power storage batteries, as well as other necessary components like battery chargers. are all available on the Renogy store.

Related articles:

AGM Battery Disadvantages

Here are two common drawbacks of using AGM batteries:

Sensitive to Overcharging

The AGM battery has a lower tolerance to overcharging and high voltages when compared to a flooded cell battery.


AGM batteries are more expensive than traditional batteries as they cost more to manufacture. On average, a conventional battery costs 65-130, but an AGM can be over 200.

Now that you know what AGM batteries are, including their pros and cons, let’s go over some FAQs.

AGM Battery FAQs

Here are some answers to commonly-asked AGM battery questions:

Are AGM and Gel Batteries the Same?

The AGM and the gel battery are often mistaken to be the same because they’re both “dry cell” lead acid batteries.

And while the gel cell is also a VRLA battery, it holds its electrolyte solution very differently.

Where the AGM battery uses an absorbent glass mat, the gel cell battery uses a chemical agent (like silica) to suspend the electrolyte in a gel form. The gel restricts movement, so the battery becomes spill-proof.

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Gel batteries don’t do as well as the AGM as a starter battery, so you’re less likely to find them performing that function in cars.

Are AGM Batteries Deep Cycle?

AGM technology is used in both deep cycle and starter battery application.

“Deep cycle” is defined by plate thickness and not the battery technology, so an AGM deep cycle battery is used as often as a flooded or gel cell deep cycle battery.

What Are Flooded and Sealed Lead Acid Batteries?

In a flooded lead acid battery (FLA), the lead plates are suspended in a free-flowing liquid electrolyte. It’s a wet cell battery, meaning the battery can spill and requires regular electrolyte maintenance.

A conventional flooded battery often refers to a flooded lead acid battery.

The sealed lead acid battery (SLA battery) applies similar chemistry. But unlike a traditional flooded cell battery, the electrolyte in an SLA battery is suspended in a gel form (for gel cell batteries) or held by a glass mat (for AGM batteries).

How Is a Lithium Battery Different from AGM?

AGM and lithium batteries have their own benefits and drawbacks.

The lithium ion battery is much lighter, has a better cycle life, and can charge faster than the AGM battery. Lithium ion batteries also have a flat discharge curve (meaning if you power a torchlight with a lithium battery, the bulb won’t dim as battery power runs out, it’ll just go off).

However, AGM batteries are cheaper to produce, have a higher Cold Cranking Amps (CCA) rating, and are resistant to vibration.

It’s important to know that you can’t just swap the AGM starter battery in your car with a lithium ion battery, as your charging system probably isn’t set up to charge a lithium battery.

Tip: Always consult a mechanic on what battery type to use if you’re unsure.

Can I Charge an AGM Battery with a Regular Battery Charger?

AGM batteries are sensitive to overcharging, which can affect their battery life. So, a regulated battery charger or battery maintainer is a key battery accessory you should use.

The right AGM battery maintainer typically has microprocessors that adjust the current and voltage delivered to the battery to avoid overcharging.

Do AGM Batteries Work with Solar Panels?

An AGM battery can be used as a solar battery. You can use a solar panel to charge one, and they’re well-suited for applications with low energy demands.

However, keep in mind that:

  • The solar panels should provide sufficient voltage (V) to charge the AGM battery.
  • You’ll need to use it alongside a solar charge controller. The solar charge controller is a battery accessory that regulates the charge to avoid battery damage.

AGM batteries have a relatively low upfront cost compared to lithium ion batteries, which are better for high energy draws in residential solar panels.

What Is a Start-Stop Vehicle?

Start-stop vehicle technology automatically turns off the engine when the car stops (like at traffic lights or in stop-and-go traffic).

While the engine is temporarily off, the car battery is the sole source of power to all the vehicle’s electrical devices, from stereo to GPS navigation. When the clutch is depressed or the brake pedal is released, it restarts the vehicle quickly and quietly.

AGM batteries are well suited for such demanding applications.

What Is Battery Internal Resistance?

Internal resistance denotes a battery’s ability to deliver high currents without a significant voltage drop.

Any current that doesn’t go into the charging translates into heat, which is why batteries get warm during heavy charging. In extreme cases, a thermal runaway can occur.

New flooded lead acid batteries typically have 10-15% internal resistance, while a gel battery has around 12-16%. AGM batteries have among the lowest internal resistance in commercial batteries, with some as low as 2% in new batteries.

Final Thoughts

As vehicles evolved and developed greater power demands, battery technology had to evolve to meet these power needs. And when it comes to meeting advanced power needs, the AGM battery is currently the best one among all lead acid options.

If you are facing any issues with your existing flooded lead acid or AGM battery or have any other battery concerns, you can always look to RepairSmith for help.

Just contact us, and our expert technicians will be in your driveway to lend a hand!

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