Specifications

10
Figure 2 - Typical Construction of a Lead Acid Battery
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These disadvantages are in effect advantages of VRLA batteries. VRLA batteries are
more accepting of vibrations and being moved around a lot due to their pancake stack
like design. They can be also mounted in any orientation and can‟t be spilled because
their electrolyte is immobile. In addition, VRLA batteries tend to have a higher storage
capacity, a lower internal resistance, a higher charging efficiency, and are maintenance
free. VLRA batteries, however, are much more sensitive to overcharging than flooded
cell are. This is because they are sealed electrolyte is immobile, thus extra cannot be
included in the design. So the only disadvantages of VRLA batteries when compared to
flooded cell batteries are price, lifespan and sensitivity to overcharging. In general,
VRLA batteries are about twice the cost of a comparable sized flooded battery, but their
lifespan is only slightly less if charged correctly every time.
Valve regulated lead acid batteries are batteries that are in most cases sealed.
However, if the pressure inside the battery gets too high due to hydrogen and oxygen
created by electrolysis within the battery, a safety valve will open and relieve the
pressure. When this happens, the water is permanently lost to the battery. However, in
most cases, the pressure never builds high enough within the battery to open the valve.
This keeps the hydrogen and oxygen inside the battery, so that it can later recombine to
form water again. There are two types of VRLA batteries; the gel battery (gel cell) and
the absorbed glass matt (AGM) battery. Gel batteries are exactly what they sound like.
The electrolyte in gel cells is gelified, and practically immobile. Other than that, they use
basically the same chemistry as a flooded cell. AGM batteries hold the electrolyte in a
glass mat between the lead plates. During the manufacturing of the battery, the glass
matt is soaked in the electrolyte, and then slightly wrung out, making the battery
capable of holding more acid than is available and therefore practically spill proof. But
again, the chemistry is still basically the same as that applied by a flooded cell. The
different constructions of these two batteries results in some important end
characteristic differences. AGM batteries have a lower internal resistance, which results