There are two main methods of discharging batteries: manual discharge techniques and using electronic loads. Depending on your application, one method may be more suitable than the other.
Deeply discharging a lead acid battery damages it so doing that for the sake of doing that doesn't sound like a good idea. And if you have some reasonable usecase for that then you'd better explain so that answers can address your actual problem. A discharged lead-acid battery can hardly be considered safe.
Figure 4 : Chemical Action During Discharge When a lead-acid battery is discharged, the electrolyte divides into H 2 and SO 4 combine with some of the oxygen that is formed on the positive plate to produce water (H 2 O), and thereby reduces the amount of acid in the electrolyte.
How a lead-acid battery is charged?
The Charging begins when the Charger is connected at the positive and negative terminal. the lead-acid battery converts the lead sulfate (PbSO 4) at the negative electrode to lead (Pb) and At the positive terminal, the reaction converts the lead sulfate (PbSO 4) to lead oxide. The chemical reactions revers from discharging process
The Discharge of the lead-acid battery causes the formation of lead sulfate (PbSO 4) crystals at both the positive electrode (cathode) and the negative electrode (anode), and release electrons due to the change in valence charge of the lead. This formation of lead sulfate uses sulfate from sulfuric acid which is an electrolyte in the battery.
Specifically, if you want to fully discharge a typical car battery (12V, 60 A hr), all you need is a 20 ohm, 10 W resistor (or equivalent), and connect it across the battery terminals. Leave it connected for about 4 days, and with a voltmeter verify that the voltage is zero.
The following are the indications which show whether the given lead-acid battery is fully charged or not. Voltage : During charging, the terminal voltage of a lead-acid cell When the terminal voltage of lead-acid battery rises to 2.5 V per cell, the battery is considered to be fully charged.