Sulfation is one of the most common causes of performance loss in forklift batteries . It often begins at a discharge level of 30–40% and gradually leads to decreasing capacity, increased heat generation, and longer charging times. Professional desulfation can restore up to 80% of the original capacity – and avoid high replacement costs.
This guide explains what sulfation is , how to recognize it , which methods are used for desulfation, and when the effort is economically worthwhile .
What does desulfation mean?
Desulfation refers to the dissolution of lead sulfate crystals that form on the plates of lead-acid batteries. These crystals form when the battery remains partially discharged for extended periods or is not fully charged . Through targeted charging pulses or chemical recalcification , these crystals are converted back into soluble compounds – the battery regains capacity and reaction rate.
Why does sulfation occur?
Sulfation occurs due to a persistent imbalance between the electrolyte and the active material. Lead sulfate begins to solidify even during discharges above 60–70% SOC (state of charge). Typical causes include:
- Incomplete charging cycles or charging interruptions without charge completion detection
- Longer periods of inactivity without trickle charging
- Lack of temperature compensation at high ambient temperatures
- Excessive deep discharges below 20% SOC
How can you recognize a sulfated battery?
Sulfated batteries exhibit typical performance deviations. Objective measurements are crucial:
- Resting voltage below 2.1 V/cell – indication of partial sulfation
- Voltage under load below 2.0 V/cell – critical indicator
- Internal resistance ≥ 50 mΩ/cell according to impedance measurement
- Electrolyte density below 1.28 kg/l or noticeable turbidity
- Increased charging temperature above 45 °C
Diagnostic tip: Use an impedance spectrum analysis (EIS) every six months to detect crystalline deposits early. Additionally, monitoring the pH and temperature of the electrolyte is recommended to ensure correct charging parameters.
What are the consequences of sulfation?
As crystal formation increases, the usable electrode surface area decreases. This raises the internal resistance, reduces charge acceptance, and causes the battery to heat up more. A crystal volume exceeding 20–25% is considered the economic limit – above this level , regeneration or replacement is usually more practical than simple desulfation.
methods for desulfation
Two main methods are currently used for desulfation: pulsed charging cycles and chemical realkalization . Both methods should only be carried out by specialist companies with suitable measuring equipment.
Pulsed desulfation
This process uses short charging and resting phases in a ratio of 1:2 to 1:3 – typically 5 s charging / 10 s resting at a current ≤ 0.05 C. Modern desulfation devices control these pulses adaptively based on impedance feedback to efficiently and gently dissolve sulfate crystals. Conventional IUoU chargers can only partially remove sulfate.
Chemical realization
In cases of advanced sulfation, a realkalization procedure is performed. This involves adding 0.1–0.2 g/L of sodium hydroxide (NaOH) to the electrolyte. The pH is then precisely adjusted to 6.8–7.2 to protect the lead plates and neutralize any remaining sulfates. The pH is monitored using a pH meter to prevent over-alkalization.
Process duration and procedure
A professional desulfation process involves several steps:
- Diagnosis: Measurement of voltage, internal resistance, electrolyte density and EIS.
- Treatment: Pulsed charging cycles or chemical realkalization with documented parameters.
- Validation: Final measurement to determine residual capacity and cell balance.
Depending on the degree of sulfation, the process takes between 1 and 5 days . For highly consolidated crystals, several cycles are necessary. Annual recalcification and semi-annual EIS analyses are recommended as maintenance measures.
Economic efficiency and cost comparison
Desulfation is particularly economically attractive if the battery is structurally intact:
- New forklift battery: €4,000–€8,000
- Professional desulfation: approx. 30% of the new purchase price
- Up to 70% cost savings compared to new purchase
Additionally, energy consumption during charging decreases by 10–15% . The investment typically pays for itself after 3–6 months of operation. Replacement becomes more economically viable when the crystal volume exceeds 25% .
Practical examples and success rates
In practice, desulfated batteries achieve 70–95% of their original capacity, depending on the type. Particularly good results are achieved with traction batteries (PzS, PzB) . Regular desulfation can extend their lifespan by a factor of 2–3 . In cases of extreme sulfation, the process can take up to 5 days , but is successful in many cases.
Relevant norms and safety standards
- DIN EN 62485-3: Safety requirements for battery charging systems
- DIN EN 50272-2/3: Safety requirements for stationary batteries
- DGUV Regulation 68/69: Industrial trucks and battery systems
- VdS 2259: Battery charging equipment
- FBRCI-013: Explosion protection at battery charging stations
Safety and environmental aspects
Strict occupational safety regulations apply to the chemical treatment of batteries. Sulfuric acid is highly corrosive (pH ≈ 0.5). Safety goggles, acid-resistant gloves, and an apron are mandatory. The rooms must be well-ventilated (at least 2.5 air changes per hour). Fire extinguishers (CO₂ powder) are required because explosive gas can be produced.
Environmental aspects are also relevant: Lead is almost 100% recyclable . Desulfation significantly reduces CO₂ emissions, as no energy-intensive new production is required. Residues are disposed of in accordance with the German Battery Act (BattG) .
Influence of temperature
High temperatures significantly accelerate sulfation. Even 10 °C above the standard operating temperature halves the lifespan. Cold storage conditions, on the other hand, slow down the process but reduce the charge acceptance. The ideal operating temperature is 20–25 °C . A voltage compensation of −24 mV/°C per cell is recommended.
Diagnostic procedures and measurement technology
The following measurements are crucial for a precise condition analysis:
- EIS analysis (impedance spectrum): detects crystalline deposits at an early stage
- Internal resistance measurement: An increase above 50 mΩ/cell indicates sulfation.
- Electrolyte density & pH value: below 1.28 kg/l or outside 6.8–7.2 critical
- Temperature sensors in the cell: important for precise compensation
Shelf life after desulfation
After successful desulfation, a further service life of 2–4 years is realistic. With regular maintenance (EIS analysis, realkalization, float charging), the overall service life can be extended by a factor of 2–3 . Specialized companies document capacity values and often offer a warranty on regeneration .
Alternatives to desulfation
If the battery is severely damaged (crystal volume > 25%), replacement may be more economical. Alternatives:
- Used batteries with tested remaining capacity
- AGM or gel batteries – maintenance-free, but more expensive
- Lithium-ion systems – 3–5 × longer lifespan, less maintenance required
However, in cases of moderate sulfation, regeneration usually remains the most cost-effective and environmentally friendly solution .
How can sulfation be prevented?
- Daily maintenance charge at 2.23–2.30 V/cell
- Avoid deep discharges above 60% SOC
- Monthly pulse discharge for cell activation
- Annual recalculation and pH control
- Semi-annual EIS analysis for early detection
Conclusion: Recognize sulfation early and treat it professionally.
Sulfation is not irreversible damage – but it is a serious warning sign. Adaptive pulse desulfation , pH-controlled realkalization , and consistent maintenance can significantly extend the lifespan of your forklift batteries and ensure their long-term performance.
HK Handels GmbH offers professional desulfation, regeneration and maintenance services for forklift batteries – including precise diagnostics, certified procedures and comprehensive documentation for maximum cost-effectiveness.
