Techniques for VRLA Batteries

In a flooded lead-acid system, the two plates charge independently of one another due to the saturated electrolyte condition and to the low diffusion rates of oxygen and hydrogen gases in sulfuric acid. Thus, these gases escape from the cell before they can interact with the opposite electrode. Both are still affected by impurity effects on overpotentials and thus perfectly efficient recharge of both plates is not guaranteed. 

In practice, the negative electrode assumes a mixed-potential condition, with some portions of the surface supporting oxygen reduction and others continuing to generate hydrogen gas, as shown in Fig. 9.2. This is a balanced, delicate condition, and small changes in saturation levels or choices of separator characteristics can 

---