# Sulphation

> Crystallisation of lead sulphate on the plates when the battery spends time discharged. Reduces capacity irreversibly.

**Categoría**: Maintenance & use
**URL canónica**: https://baterias.com/gb/battery-glossary/sulphation
**Idioma**: en-GB

## Definition

Sulphation is the formation of large, hard lead sulphate (PbSO₄) crystals on the battery plates. It is the #1 cause of premature death in lead-acid batteries. During normal charge/discharge cycling, lead sulphate appears and disappears reversibly; but **if the battery spends days or weeks below 50% SOC the crystals grow large and insulating** — they block the active surface of the plates and permanently reduce the ability to accept current. Typical causes: leaving the car parked for months without use, motorcycle batteries in winter, systems with an undersized alternator, batteries drained by vehicle parasitic loads (alarm, GPS, keyless entry). Prevention: **trickle charger if the vehicle goes more than 3 weeks without being started**. Symptoms: low SOH, normal open-circuit voltage (12.6 V) but collapsed CCA on starting. Some smart chargers offer a "desulphation" mode (high-frequency pulses) that can reverse early sulphation — it only works on light cases, not on advanced sulphation.

## See also

- [SOH (State of Health)](https://baterias.com/gb/battery-glossary/soh)
- [SOC (State of Charge)](https://baterias.com/gb/battery-glossary/soc)
- [Smart charger](https://baterias.com/gb/battery-glossary/smart-charger)

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