What is battery desulfation

Battery characteristics & fault diagnosis

Yuasa lead-acid batteries are manufactured to the highest standards so that in most cases they will meet or exceed the vehicle manufacturer's requirements and specifications.

It must be clear, however, that wet (filled) lead-acid batteries are “living” products. Whether in storage or in use, a battery has a finite lifespan. All batteries slowly self-discharge after filling. The higher the storage temperature and humidity in the warehouse, the higher the self-discharge rate.

To prevent batteries from discharging to the point that they are damaged (sulfation) or cannot achieve the expected service life, the charge date label on the back of the battery must be checked regularly. Voltage tests should be performed on batteries that are due to be charged in less than 4 months. A good inventory turnover according to "first in, first out" must be practiced, especially with slow-moving inventory of product lines manufactured in small quantities. Batteries with a voltage of 12.35 V or less should be charged immediately. Do not use a quick charger to charge as this device is inefficient at charging a partially sulfated battery. This leads to excessive gas formation and damage to the grid connections of the active material in the battery, which are necessary to ensure the battery life.

Ideally, you should use the “recommended charge rate and duration” given in the battery type and catalog instructions. At the end of the discharge, all cells should release gas. It is clearly recommended that batteries are left to rest for at least 3 hours after charging to ensure that any gases trapped in the upper part of the battery case can escape to the atmosphere. When the battery has been charged, the charging date on the label on the back of the battery should be indented to extend the charging date by 6 months after the second charging date. (Please note that a maximum of two top-ups are allowed before sale and that the product must be sold a maximum of 9 months after the first recommended top-up date).

Battery problems

No manufacturing defects

Physical damage

If the battery is improperly stored, handled or installed, if the connecting cables are hammered into the terminals, if cables are not fastened correctly, the battery housing and / or the terminals will be damaged. This is not a manufacturing defect.
* Please note that all batteries packed and shipped from Yuasa UK warehouse will be photographed prior to shipment so we can ensure our shipping quality goals are met.


If a battery is discharged for a long time in or outside a vehicle, a chemical reaction takes place, which irrevocably affects the performance and service life of the battery. This process is called "sulfation".

Sulphation can be recognized by a slight white / gray deposit on the positive plate and a non-metallic sheen on the negative plate. In most cases this means that the battery is unusable. Attempts to recharge batteries that have been in a discharged state for a long time can damage the grid and active material, even at low charge rates. In addition, sulphate deposits can form in the separators and cause dendritic short circuits.

The damage can occur during storage or if the battery is installed in a vehicle (or device) that will not be used for an extended period of time, such as a tractor, motorcycle, boat, airport vehicle, or even a car or truck if connected to it Battery. This is due to the fact that the battery is used up by turned on functions such as alarm, clock, lighting etc. until it reaches its lowest charge level. The longer this condition lasts, the greater the sulphate deposits on the plates.

The sulfation affects the efficiency of the electrochemical reactions in the battery between the active material of the plates and the acid. This is not a manufacturing defect.


When a battery goes through a cycle, i.e. when it is charged and discharged, the active material in the battery plates is in motion to release the electricity stored in the battery. Every time the battery charges and discharges, a small amount of the active material is lost from the plates forever.

Since the actual battery life depends on numerous factors, for example temperature, state of charge for battery operation, duty cycle, etc., no minimum / maximum life expectancy can be specified here. The normal aging process will ultimately cause the battery to lose power and the moment will come when the battery can no longer start the vehicle or device. The modern injection vehicles start much faster, for which they mostly use a surface drain from the battery plates. As a result, battery failures occur more frequently when the battery is exposed to stress, for example on a cold morning or after it has not been used for the weekend. This is not a manufacturing defect.

It is advisable to take advantage of the free battery check before the start of the cold season or before long parking periods at the airport.

Deep discharge

As above, every time a battery charges or discharges, a small amount of the material is lost. If the battery is deeply discharged (greater than 35%) and rapid charging is performed, the process will accelerate. In addition, if the charge does not completely reverse the discharge cycle, the battery will lose power and levels of acid may develop between the plates, causing corrosion and loss of performance.

Even after charging, voltage will be low (below 12.4 V), but when the acid densities of the cells are checked they are usually the same throughout the battery. This is not a manufacturing defect.


If the alternator regulator is improperly set or if the voltage circuit fails, the battery will be exposed to excessive charge.

If the battery is not checked, it will overheat and evaporate the electrolyte. Overcharging accelerates the deterioration of the active material and grids and the battery loses performance. Checking the battery will usually reveal a low acid level and black build-up on the filler cap, and a strong odor. It is recommended that a mechanic check the charging voltage of the alternator. This is not a manufacturing defect.

Wrong claim

To keep fraudulent claims to a minimum, each Yuasa battery has its own unique number on the back label. It is advisable to leave this number and proof of purchase at the point of purchase so that double checks can be carried out during the complaint process. The label is forgery-proof.

Incorrect application

The batteries recommended in this Yuasa application list meet or exceed OEM specifications. If a smaller or less powerful battery is installed, this leads to a shorter service life and an earlier failure. The failure usually comes in the form of deep discharge / premature wear.

Please note that a vehicle in which the manufacturer has installed an AGM battery should only be equipped with AGM batteries. Likewise, a vehicle originally equipped with an EFB battery should only have EFB or AGM batteries.
This is not a manufacturing defect.


Undercharging means that the battery is not being charged enough to return to a fully charged state; this slowly leads to sulfation. This problem can occur if the car is only used occasionally for short trips or trips around the city. Undercharging occurs when the alternator voltage is low (13.6-13.8 volts), the alternator belt is loose, or the battery cables are worn and causing high resistance - if you are unsure, see an auto electrician.

Battery problems

Manufacturing defects

Due to the high demands on the OEM market and the technical and manufacturing standards of Yuasa batteries, there are only very few actual manufacturing defects.

Short circuit / dead cell

Usually occurs within 12 months of service life. One cell has a significantly lower specific acid density than the others. The problem cell usually boils at a high discharge, the other cells have a good specific gravity reading of 1.26 or higher. Short circuits / dead cells that occur later in life are mostly related to the recovery of a sulfated / overdischarged battery. If the root cause is sulfation, you may find different specific acid densities in the cells.

Internal breakdown

The battery has good specific gravity, but no voltage readings. Check the battery for physical damage that could have caused the internal breakdown.


If the right battery, in the right condition, is used in the right application, very few battery problems are possible. All batteries have a finite lifespan (otherwise there is no aftermarket store for batteries), the lifespan depends on the conditions under which the battery operates. Battery failures caused by sulfation, wear and tear, deep discharge or physical damage are not manufacturing defects and are not covered by the Yuasa warranty. A battery cannot discharge itself under normal operating conditions. The reason for this can usually be traced back to:

  • Malfunction in the alternator, regulator or starter motor
  • Slipping (improperly adjusted alternator charging belt)
  • Electrical faults e.g. lighting of the interior or trunk / glove compartment, problems with the ECU sensor interface where the vehicle does not switch off after it has been parked for more than five minutes, failure of the windscreen wiper motor
  • Excessive use of electrical consumers - air conditioning, stereo (incorrectly connected directly to battery), etc.
  • Long standing times without charging
  • Vehicle lights and / or hazard warning lights not switched off

If a battery is used over and over / left in a discharged state, it will eventually reach a state where it will not recover from a controlled charge. This is known as deep discharge / undercharging and is NOT a manufacturing defect. If a battery is continuously deeply discharged through stop / start driving and heavy use of the vehicle consumer devices and then not adequately charged, it will lose power relatively quickly. This is a deep discharge / wear and tear and not a manufacturing defect. Alternative battery technologies, charging and handling solutions must be found for these applications.

CCA tests with digital conductivity battery testers.
There are various handheld digital conductance testers on the market. They usually give a fairly good overview of the problems, but the following points should be kept in mind at all times.

  • They are not a reliable method for testing the fully developed cold start capability of a NEW battery, due in part to the health measurement algorithm used. They are suitable for testing and assessing defective or used batteries.
  • Testers from different brands, and even different models from the same brand, may show different results.
  • Different design techniques used in battery production can have a significant impact on the measured values ​​of the digital conductance testers, since generally applicable algorithms have to be used. For example, batteries that are developed for higher load capacities have more material and a higher density, which can usually be recognized by a lower initial voltage and therefore longer discharge times. Digital testers can only realistically determine the initial internal resistance of the battery in the current state of the battery, not how much material is available. This can lead to considerable differences between the specified CCA data and the actual CCA data determined in the laboratory with real current loads specified according to the battery standard.
  • CCA values ​​can be measured according to a number of international standards, SAE, EN, DIN or IEC. Two requirements are listed in the EN 50342: 2006 standard: EN1 & EN2. Normal conductance testers are calibrated according to the EN2 standard, but the ETN numbering system makes it difficult for the normal person to understand which standard is used for the battery.
  • The condition of the battery cables and terminal connections can affect the measurement results of a portable tester.
  • A 2-3 year old battery may be operational for several years, but due to "wear and tear" the health measurement may only be 75%. Conversely, a deeply discharged battery (or with a partial internal breakdown) may give a good reading on the CCA scale, but may be in poor condition when verifying actual high performance or capacity. NB: If deep discharge is suspected as the reason for failure, a test in conjunction with a charge tester should be considered.

Overall, the digital conductance tester does the best at evaluating suspect or waste batteries in the market today, but you should keep the above points in mind while taking measurements.