During a discharge phase, the electrolyte reacts with the active materials of the plates, transforming both the lead dioxide of the positives and the spongy lead of the negatives into LEAD SULPHATE PbSO4. Sulfuric acid is consumed as the discharge progresses. In addition, water is formed.
The discharge process causes a drop in the voltage value, dependent on the intensity of the discharge current, which becomes rapid when the end-of-discharge voltage value is reached, beyond which it is not recommended to proceed.
This voltage value is called the End Of Life Voltage or Cutoff Voltage and for lead batteries at 25 ° C the following applies: EOLV (25 ° C) = 1.7 ¸ 1.8 VPC corresponding to a discharge equal to 100 % of the rated rated capacity in a constant current regime; the interval is a function of the discharge rate as already observed.
Deep discharge is defined as a discharge process below the cut off voltage of 1.7¸1.8 VPC.
Overdischarge is defined as a discharge beyond the deep discharge. In this case, due to the low solubility of the lead sulphate salt, lead sulphate crystals are formed on the electrodes of considerable size and irreversible at normal charge; it says that the battery is “SULPHATED”.
Sulfation (crystallization of lead sulphate) can also occur due to internal short circuits of the elements or too high density of the electrolyte or insufficient charges that are repeated for long periods of use. To eliminate sulphation it is possible to subject the elements involved to a particular treatment, consisting of LENS charges followed by discharges and interspersed with a rest period. www.tcechargers.com