GEL and AGM VRLA Battery Construction

GEL and AGM VRLA Battery Construction

AGM VRLA Battery Construction

As shown in Figure 1, the AGM VRLA battery utilizes a separator of glass fibers which serves to both isolate the negative and positive plates and act as a blotter to absorb the free electrolyte within the cell. This AGM separator is somewhat fragile, highly porous and absorbent, and has very low resistance. The AGM separator is maintained under compression between the plates to assure complete contact with the plate surface since it provides the source of the electrolyte essential to the cell’s electrochemical reaction. Actually, the separator is not completely saturated with electrolyte and it is the 2 to 10% void space which allows the oxygen gas generation from the positive plate to diffuse to the negative plate where the oxygen recombination cycle occurs. This system is also occasionally referred to as a starved electrolyte system in that there is more plate active material than that which the limited amount of electrolyte can fully react.

Figure 1 AGM VRLA Battery Construction

GEL VRLA Battery Construction

The gelled electrolyte VRLA battery, as shown in Figure 2, utilizes a robust microporous polyethylene separator. This separator is not relied upon to absorb the electrolyte since the electrolyte is gelled, but strictly performs the function of separating the plates and resisting the development of shorts between the plates. This durable separator and the gelled electrolyte are of relatively high resistance and introduce additional voltage drop during high rate discharges. The cell is completely filled to the top of the plates with the gelled electrolyte. However, there are cracks and fissures in the gel between the plates that allow the transport of the oxygen from the positive to the negative plate allowing for the oxygen recombination cycle.

Figure 2 GEL Battery Construction