This type of valve regulated lead acid battery represents
the latest development for traction applications and requires
the most performance from the separator. Contrary to
flooded cells, the oxygen generated at the positive electrode
after 80% charge, has to reach the negative plate through
micro-cracks in the gel structure and through the separator’s
void space in order to be reduced and react with protons to
form water again. Ideally, no separator should be added in
this type of battery, as the electrical resistance of the gelled
electrolyte is already quite high. However, a separator is needed to keep inter plate spacing and also to prevent any
short circuit due to plate contact or dendrite growth. Therefore,
the separator should have as low electrical resistance as
possible and very high porosity, with a structure allowing
oxygen transfer and an homogeneous internal oxygen cycle