The specificity of a calcium battery does not allow you to install it on a car and forget about it for 5 years. Problems regularly arise with it - it does not charge to 100%, suddenly loses capacity and starting characteristics, freezes, dies from a short circuit of the cells... This material is dedicated to the most common "disease" of Ca/Ca batteries - when after normal recharging the electrolyte density is much less than 1.27...1.28 g/cm3.


This article is one of many on the Auto without a service station website, written based on my personal experience. In 2021, material was published about recharging a calcium battery, which was only 2 years old at the time. Now it's 2024 and this battery is still in service. That is, she is already 5 years old. The battery is used in very unfavorable conditions. I drive a car a little and not far. The battery does not have time to fully charge from the generator. Therefore, as an informed user, I regularly recharge it using a stationary charger.

Note. At first I had at my disposal a homemade power supply with the ability to adjust the voltage. It was this device that appeared in the master class on recharging 3 years ago. Now I have a new “combine”, assembled on the basis of RIDEN RD6006P and ATORCH DL24 modules. The first is a precision laboratory power supply. The second is a popular inexpensive electronic load. By combining these two modules, I received a multifunctional device for servicing and testing batteries.

It's winter now. Difficult period for a car. Especially for batteries. Right on New Year's Eve, my car let me down - it refused to start. From experience, I immediately determined that the problem was in the starter. It made one clicking sound and nothing else happened. Battery voltage is normal. There is no sag when starting the engine.

Since I had no desire to tinker with the starter during the New Year holidays, I took it to a local auto electrician for diagnostics and repairs. Given the time of year, he promised to return it in two days. In order not to waste time, I decided to pay attention to my 5-year-old battery. And this is where trouble awaited me.

I removed the battery from the car and first of all cleaned the case of dust and dirt. I charged it with my “combine” the way I described it long ago in an article about charging calcium batteries. Since I had time (the starter was still under repair), I decided to discharge the battery in order to check the actual capacity and assess the condition of the “old man”.

Note. I measure the capacity of all batteries that pass through my hands (for example, this new battery) as written in the current GOST. That is, I discharge with a current of 0.05 C to a voltage of 10.5 V. I categorically do not recommend doing this constantly with the same battery, since deep discharges have a detrimental effect on the life of calcium batteries. Discharge to 12.0 V, and multiply the resulting capacity value by 2. The difference will be at the level of measurement error.

The electronic load showed a capacity of only 17 A*h! This is at a nominal value of 60 A*h. Yes, the battery is 5 years old. But with such indicators, he should not turn the starter at all. And he coped with this job 100% even in severe frost.

I decided to charge the battery in the usual way and check the density of the electrolyte. Charged. By the way, the battery took almost the same 17 A*h. A little more. I measure the electrolyte density in all cells, and immediately understand what the problem is...

You will find out the end of this story later, in the process of familiarizing yourself with the material.

Signs of a problem

Modern car enthusiasts very rarely measure the density of the electrolyte. Even if the battery design allows this. Many generally have maintenance-free batteries installed, the density of the electrolyte in which is generally impossible to estimate. Happy people…

Most often, a hydrometer is remembered precisely in situations such as those that I described in the background. The battery is removed from the car and charged in the usual way or even with an automatic charger. Everything seemed to go fine, but... The charging process ended too quickly. Not in 18-20 hours, but in 4-6 hours (read my material about battery charging time). This should already be alarming. For batteries with a built-in indicator, it does not turn green, remaining white or even red.

You take a hydrometer and measure the density of the electrolyte. And the device shows only 1.2 g/cm3, which corresponds to a charge level of no more than 50%. How so? After all, the battery is charged. The voltage reached the required 14.4-14.8 V, and the charging current dropped to 0.1-0.3 A.

Why is the density not 1.28 g/cm3?

What should you not rush to do?

Often, after a superficial study of the problem, car enthusiasts in such situations rush to attempt to adjust the electrolyte density in the following ways:

  • pumping out part of the electrolyte and adding so-called correction electrolyte;
  • the same thing, but with the addition of concentrated sulfuric acid;
  • pumping out all the electrolyte present in the battery and filling it with fresh, normal density.

Even professional battery technicians periodically resort to these methods. But they also say every time that in the current realities such manipulations should be avoided to the last. To the point where it’s better not to suffer right away and buy a new battery. I have also held the same opinion for many years, and have repeatedly been convinced that it is reasonable. Especially if you are well versed in modern battery manufacturing technologies and the resulting operational features.

Don't rush either. Do not run to the nearest auto shop for correction electrolyte or concentrated sulfuric acid. In 90% of cases, this will end with you going to the auto store again. But already for a new battery.

Possible reasons

Before jumping to conclusions, make sure that:

  • in all battery compartments there is a normal electrolyte level (at least 15-20 mm from the plates);
  • you just did not add distilled water to the battery;
  • the battery was charged from a stationary charger;
  • no signs of short circuit;
  • the electrolyte is transparent (not cloudy, not black, not brown).

If the electrolyte level is below normal, it must be replenished with distilled water. After this, be sure to charge the battery again as described in the articles linked above.

If there are signs of a short circuit (you can learn about them from this material) or the electrolyte in the battery is not transparent, you can close this page. It’s better to read how to choose a new battery and whether it needs to be charged before installing it in a car.

If everything is as it should, but the density of the electrolyte is around 1.2 g/cm3, then most often this is preceded by the following reasons:

  1. Incorrect charge.
  2. Electrolyte separation.
  3. Sulfation.

Note. In my case it turned out to be sulfation. This is the most complex and unpleasant phenomenon of the three listed. The electrolyte density in all cells is 1.2 g/cm3. The charging indicator is not even white, but red. I rule out an incorrect charge because I am confident in my knowledge of the battery and in my equipment. I also ruled out electrolyte separation. You will learn further how to determine the cause of low electrolyte density in your battery. And you will also learn what to do about it.

Incorrect battery charge

There are several ways to charge a battery incorrectly. The first is to use a simple automatic or “smart” charger. As a rule, such devices turn off earlier than necessary, indicating on the display that the battery is 100% charged. The second way is to charge with cheap chargers, which have nothing inside except a transformer and two diodes.

Usually, if you do everything correctly, the electrolyte density is either normal or not far from it. If the hydrometer stubbornly shows no more than 1.2 g/cm3, then the reason is definitely not in the charging algorithm.

Electrolyte separation

Note. The electrolyte in lead batteries consists of two components - water and sulfuric acid. By measuring density, we estimate the concentration of sulfuric acid dissolved in water. The smaller it is, the lower the density. During the battery discharge process, acid “sticks” to the lead plates in the form of lead sulfate. When we charge a battery, the acid “leaves” the plates, dissolving in the electrolyte and increasing its density.

Sulfuric acid is heavier than water. Despite the fact that it dissolves well in water, it tends to sink under the influence of gravity to the bottom of the battery. As a result, the density of the electrolyte in the upper layers decreases, and in the lower layers, on the contrary, increases. This phenomenon is called stratification or stratification of the electrolyte.

Since we use a hydrometer to take the electrolyte from the upper layers, if there is stratification, its readings may well be underestimated. However, there is one important feature here. The difference between the density of the “upper” and “lower” electrolyte in the case of stratification is insignificant. Usually 0.01-0.03 g/cm3, no more. If the density of the electrolyte in a charged battery is about 1.2 g/cm3, then most likely the reason is not delamination.

Note. How do I eliminate delamination? Firstly, due to the too low density of the electrolyte taken from the upper layers with a conventional hydrometer. Secondly, I take electrolytes from the bottom of the battery and compare the values. To get the “bottom” electrolyte, just attach a thin tube (I use a WD-40 tube) to a syringe, pipette or hydrometer. Since I charged my battery and then mixed the electrolyte, the density of the “lower” and “upper” electrolyte turned out to be equal - 1.2 g/cm3.

If in your case, however, there are signs of stratification, methods for eliminating it are described in the materials on recharging a calcium battery and the charge indicator on the Auto without a service station website.


Sulfation is normal for a lead-acid battery. It always occurs when the battery is discharged. However, there is such a thing as irreversible sulfation. This is when the lead sulfate on the plates does not disintegrate during the charging process. This happens with sulfate that has been on the plates for too long. As a result, the crystals became larger and hardened. When charging batteries normally, they are not destroyed. Accordingly, sulfuric acid is not returned to the electrolyte, which is why its density does not increase to normal.

You can diagnose sulfation in two simple ways:

  1. Charge the battery and measure the density of the electrolyte. If the hydrometer readings are far from normal, this is a sign of irreversible sulfation.
  2. Look at the plates inside the battery after charging. If a light gray coating is clearly visible on them, then this is undissolved lead sulfate.

Why is sulfation bad?

Firstly, the battery is not able to accumulate the amount of energy for which it is designed. In other words, instead of 60 A*h, it can accumulate, as in my case, only 17 A*h. The second figure depends on how long ago irreversible sulfation began and under what conditions this occurred.

Secondly, the starting characteristics of the battery are reduced. Instead of the 400-700 A starting current stated on the label, it will produce several times less. In good frost, this may not be enough to move the starter and start the engine.

Thirdly, the freezing point of the electrolyte increases, since it contains a weak concentration of acid. And freezing of the battery often results in a short circuit, deformation of the plates and destruction of the case. If the freezing point of an electrolyte with a density of 1.265 g/cm3 is -60 degrees Celsius, then at a density of 1.2 g/cm3 it will begin to turn into ice at -24 degrees below zero.

How to properly charge the battery?

To charge the battery correctly, you need to:

  1. Know his type.
  2. Have a charger with the ability to adjust and control charge parameters.
  3. Charge at least as described in the materials corresponding to the battery type on the Auto without a service station website.

A charge performed in accordance with the operating instructions for a specific battery can also be considered correct.

How to eliminate electrolyte separation?

To eliminate electrolyte separation, it must be stirred. The simplest and most correct way to do this is to apply a voltage of 16.2-16.5 V to a charged battery for 40-60 minutes. You can also collect a denser electrolyte at the bottom of the battery and pour it on top. However, the second method should not be used if your battery is more than 3 years old. At its bottom, most likely, there is a lot of debris, the contact of which with the plates can lead to a short circuit.

I categorically do not recommend how to eliminate electrolyte separation? There is no need to try to mix the electrolyte by shaking or rocking the battery. Under no circumstances should you turn the battery over to drain all the electrolyte, mix it in a container and pour it back in.

How to perform desulfation?

The most adequate way to increase the density of the electrolyte is desulfation. I already described this event a couple of years ago. However, during this time I gained new knowledge and fresh personal experience. Therefore, consider this material more relevant than my old article on desulfation (although it is also quite good).

For now, I suggest exploring three desulfation methods:

  1. Using a special charger.
  2. Classic control-training cycle.
  3. Simplified control and training cycle.

Note. Personally, I usually combine the second method with the third. However, you must understand that the time spent will greatly depend on the method you choose. I have time. I do not encourage special chargers, since I prefer to control the process myself. Therefore, I act slowly, using my “combine” for battery maintenance, mentioned above.

Special charger

This is the easiest and fastest way. But provided that the charger you purchased actually has the necessary functionality. I will not give examples of models of such devices here. My articles are read by people from different countries, and you may simply not find such titles in local online stores. I'll just briefly tell you what to look for.

By a special charger I mean a device in which the developer includes a desulfation function. Some call this process a “control-training cycle”, “training”, “recovery” of the battery. In fact, all these concepts are equivalent and chargers work according to the same algorithm. With differences in details that do not greatly affect the result.

The operating principle of such devices in desulfation mode is very simple. The device charges the battery for some time, then either stops the process or additionally discharges it. This process is called a charge-discharge cycle. The device repeats this cycle many times until the conditions set by the user in the settings are achieved. Or until the process is stopped manually. Depends on the configuration and functionality of the charger.

To perform desulfation and increase the density of the electrolyte in this way, find such a device and simply follow the instructions in the instruction manual. I repeat that this is the easiest and fastest way. But provided that the device you bought did not turn out to be a fake with primitive filling and promising inscriptions on the body.

Note. Any smart charger with a desulfation function can be easily tested. Connect it to your battery and configure it as indicated in the manufacturer's instructions. Next, take a simple multimeter, turn it on to DC voltage measurement mode and connect the probes to the battery terminals. Observe the instrument readings. If the voltage periodically increases and decreases, then there is every chance that the charger is really “training” your battery. Check even those chargers that have built-in meters. Often they do not show what is happening, but the settings you entered or the numbers specified by the program.

Classic control-training cycle

This method is a little more complicated and takes longer. To desulfate the battery and increase the electrolyte density you will need:

  1. Any charger or power supply with the ability to regulate voltage.
  2. Some kind of load to discharge the battery.

I use the electronic load of my "harvester", however, a simple 20-40 W car light bulb will do.

The classic control-training cycle can be performed in two ways.

First way. Charge the battery completely. Record the density of the electrolyte to see the dynamics. Discharge the battery with the existing load to a voltage of 12 V (this voltage should be under load, and not after it is turned off). Re-measure the electrolyte density and evaluate the result. If you are not satisfied with it, repeat the discharge-charge. If after two cycles the density has not increased at least a little, there is no point in continuing the procedure. The sulfates in your battery are so strong that they cannot be destroyed by adequate methods.

Second way. Suitable for those who have more time. Charge the battery and record the density (you may have already done this). Discharge the battery to 12V (under load). Next, alternate between charging and discharging for several minutes. For example, charge for 30 minutes, discharge for 30 minutes. At the same time, make sure that the balance between the charge and discharge current is positive. That is, so that in the end your battery is charged and stops consuming current. When the charge is complete, evaluate the density of the electrolyte and compare the results with previous readings. Repeat until there is progress or normal density is obtained.

Simplified control and training cycle

This method takes the longest. However, it allows you to do without forcibly discharging the battery. That is, you don't need an electronic load or a car light bulb. All you need is a charger or power supply with voltage regulation.

Algorithm of actions. Charge the battery as you usually do, then measure the density of the electrolyte. Leave the battery for a couple of hours. Reconnect the charger or power supply to it and repeat the charge. Measure the density of the electrolyte and compare with previous readings. There may be no progress after the first attempt. Repeat the two-hour settling and charging. Leave the battery alone at night. The next day, repeat the same.

If there were sulfates in your battery, which there is at least some chance of dissolving, then you will inevitably get positive dynamics. The only question is how long it will take you.

How do I do it?

Since I have a full-fledged laboratory power supply and an electronic load, I increase the electrolyte density using the following algorithm (remember, I have a calcium battery):

  1. I remove the battery from the car in the condition it is.
  2. I put it on charge, limiting the voltage and current - 14.7 V and 3 A.
  3. I wait until the current drops to 0.5 A.
  4. I limit the current by reducing it by 2 times (1.5 A).
  5. I increased the voltage to 16.2 V.
  6. I charge until the current remains stable for 2 hours. At this stage, it is important not to allow the electrolyte to boil too intensely. There should be moderate gas formation. Also, do not allow the battery to heat above +45 degrees Celsius. If you experience any of these, stop the process, reduce the voltage and current, then continue.
  7. I measure density and evaluate dynamics. If there is progress, I will continue.
  8. I discharge the battery with a current of 2-2.5 A for 2 hours.
  9. I repeat steps 2-7. If it's night ahead, I leave the battery alone. The next day I continued.
  10. I repeat the procedure until the density rises to normal. If after 2-3 cycles the hydrometer readings do not change, I stop mocking the battery.

What did I end up with? Let me remind you that the battery is calcium, it was used for 5 years in unfavorable conditions, but was regularly serviced. The density after the first charging using the standard method was 1.2 g/cm3.

On the first day of the “training”, due to the fact that I was often distracted by other things, I did not see any progress.

By the end of the second day, which was more productive, the electrolyte density had already risen to 1.24 g/cm3. There is much less light gray coating on the lead plates. The battery charge indicator turned white instead of red.

On the third day, the hydrometer showed 1.26 g/cm3. There was practically no plaque on the plates at all. The indicator turned green.

On the fourth day the car was in operation. The training had to be interrupted.

Only at the end of the fifth day did I see the treasured 1.27 g/cm3 on the hydrometer . The indicator is still green. No plaque is visible on the plates. I checked the electrolyte for stratification - the density is uniform throughout the battery.


By the way. Some may be wondering what happened to the starter. On the website Auto without a service station there is a material called “The starter clicks, but does not turn - 10 faults and repairs.” In my case there was fault No. 7 from this material.


As my personal experience has shown, it is quite possible to increase the density of the electrolyte (hydrometer vs refractometer) without vandalism. Of course, not all of you will get the same result. It must be understood that the likelihood of success of desulfation depends on many factors. Depending on the condition of the specific battery, existing equipment, free time... I strongly advise you to carry out battery maintenance regularly and at an ambient temperature of +20...+25 degrees Celsius. Also be prepared to spend quite a lot of time. It took me 5 days, which is an average result.

In conclusion, here is one iconic quote from an old computer game. "Have I already told you what insanity is? Insanity is the exact repetition of the same action over and over again in the hope of a change. Can you see how this relates to desulfation?