A typical lead–acid battery contains a mixture with varying concentrations of water and acid.
Lead Acid batteries have changed little since the 1880’s although improvements in materials and manufacturing methods continue to bring improvements in energy density, life and reliability. All lead acid batteries consist of flat lead plates immersed in a pool of electrolyte. Regular water addition is required for most types of lead acid batteries although low-maintenance types come with excess electrolyte calculated to compensate for water loss during a normal lifetime.
Electrochemistry
Lead Acid Battery Discharge
When you use a 12V battery with a DC stabilizer, the output is always stable at 12V. The DC stabilizer is designed for devices that do not accept an input voltage that is too high or too low. Suppose you have a device (for example a depth sounder) with an operating voltage of 10.5V-12.9V then you need to use the DC stabilizer with a lithium battery. With a “normal” lithium battery because the maximum voltage of 13.6V is above the maximum voltage of 12.9V of the depth sounder. With a battery from the AV line you need the DC stabilizer because the minimum input voltage of 10V is above the minimum voltage of 9V of the AV battery. In this case the device would switch off while there is still 25% of capacity in the battery remaining.
Negative plate reaction
Pb(s) + HSO−4(aq) → PbSO4(s) + H+(aq) + 2e−
The release of two conducting electrons gives the lead electrode a negative charge.
Positive plate reaction
PbO2(s) + HSO−4(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l)
taking advantage of the metallic conductivity of PbO2.
The total reaction as
Pb(s) + PbO2(s) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)
The net energy released per mol (207 g) of Pb(s) converted to PbSO4(s), is ca. 400 kJ, corresponding to the formation of 36 g of water.
Lead Acid Battery Charging
In the fully charged state, the negative plate consists of lead, and the positive plate is lead dioxide. The electrolyte solution has a higher concentration of aqueous sulfuric acid, which stores most of the chemical energy.
Overcharging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water, which bubbles out and is lost. The design of some types of lead acid battery allows the electrolyte level to be inspected and topped up with pure water to replace any that has been lost this way.
Effect of charge level on freezing point
Because of freezing-point depression, the electrolyte is more likely to freeze in a cold environment when the battery has a low charge and correspondingly low sulfuric acid concentration.
Ion motion
During discharge, H+produced at the negative plates moves into the electrolyte solution and is then consumed at the positive plates, while HSO−4 is consumed at both plates. The reverse occurs during charge. Therefore, a liquid-medium cell tends to rapidly discharge and rapidly charge more efficiently than an otherwise similar gel cell.
Measuring the charge level
Because the electrolyte takes part in the charge-discharge reaction, this battery has one major advantage over other chemistries: It is relatively simple to determine the state of charge by merely measuring the specific gravity of the electrolyte; the specific gravity falls as the battery discharges. Some battery designs include a simple hydrometer using colored floating balls of differing density.
Voltages for common usage
IUoU battery charging is a three-stage charging procedure for lead-acid batteries. A lead-acid battery’s nominal voltage is 2 V for each cell.
Float voltage varies depending on battery type, and ranges from 1.8 V to 2.27 V. Equalization voltage, and charging voltage for sulfated cells, can range from 2.67 V to almost 3 V.
Related Lead Acid Battery Products
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