During the conventional charging process, when battery charging is almost complete, the charging current is used solely for electrolytic decomposition of oxygen gas from the positive plates and hydrogen gas from the negative plates. The generated gas normally escapes from the battery, causing a decrease in the electrolyte , thereby requiring occasional water replenishment.
The Double Tech Batteries, however, utilize spongy lead characteristics (or negative active material) which reacts very quickly with oxygen, particularly in moist conditions. Less water is used and less is needed for replenishment.
The process of charging from its beginning to the final stage is identical with that of conventional batteries as shown in Fig 5.1.
After the charging stage or in an overcharge condition, the charging energy is used for the electrolytic decomposition of water. The positive plates generate oxygen gas, which reacts with the spongy lead in the negative plates and the sulphuric acid in the electrolyte. This turns part of the negative plates into a discharged condition thus suppressing the hydrogen gas generation.
These discharged condition negative plates are reverted to original spongy lead by subsequent charging. Thus, a negative plate keeps equilibrium between the amount which turns into spongy lead by charging and the amount of spongy lead which turns into lead sulphate through absorbing the gas generated from the positive plate. Because this entire process is self-sustaining the battery can be a sealed acid type.
The chemical reaction which takes place after the final stage of charging or under overcharge condition is an shown is Fig 5.2. and the reaction formula is described in ①-④.
The chemical reaction taking place in a lead-acid battery is as shown in the following formula:
· Fig 5.1 Reaction from beginning of charging to just prior to the Final Stage
· Fig 5.2 Reaction after Final Stage of Charging
As described above, the oxygen gas generated from the positive plates reacts quickly with the active material in charged condition in the negative plates and returns to water thus making it possible to build the battery in a sealed construction.