Their sulfuric-acid electrolyte transfers a quantity of sulfate to the plates, and recovers it respectively during these alternating phases. Lead battery sulfation impedes the flow of electrical charges when discharging, until the battery is technically ‘flat’. However, sulfation need not be permanent.
In summary at this point: Lead-acid batteries may ‘hard’-sulfate if they do not recharge in a matter of days. This is why lead batteries in storage should ‘trickle charge’ to avoid this. Undercharging a lead battery by 10% reduces its capacity by a similar factor. The longer a battery is in storage, the greater the chances of ‘hard’ sulfation.
Also, the lead–acid battery can be viewed as serving three major functions in military vehicle systems. The first is the engine start function. In this case the battery has to provide sufficient power to accelerate the rotation of the crankshaft (or fan as the case may be) to bring about a successful engine start.
In this case the natural self-discharge completely discharges the battery. This is rarely the case in commercial and passenger vehicle applications. The result of this hydration condition is that lead sulfate is dissolved as lead solubility increases considerably in the low specific gravity electrolyte.
Lead battery sulfation impedes the flow of electrical charges when discharging, until the battery is technically ‘flat’. However, sulfation need not be permanent. A lead battery goes through the sulfation / de-sulfation routine numerous times during its active life. This is because the sulfate is still ‘soft’, and almost all of it removes easily.
The reaction of lead and lead oxide with the sulfuric acid electrolyte produces a voltage. Supplying energy to an external load discharges the battery. During discharge, both plates convert to lead sulfate (PbSO 4) and the electrolytes becomes less acidic.