Valve-regulated lead-acid (VRLA) batteries are characterized by relatively
poor performance in cyclic applications of the order of two hundred to thre
e hundred 100% depth-of-discharge (DoD) cycles. Failure is due to sulfation
of the negative plate and softening of the positive active-material. It is
felt that this failure mode arises from abnormally high levels of oxygen r
ecombination that arise due to decreases in separator saturation levels as
VRLA batteries age. Charging algorithms have been developed to address this
changing condition throughout life. The key step is the finish of charge w
here, traditionally, low currents and low overcharge limits have been emplo
yed with poor results. It has been found that using high finishing currents
in an alternating charge-rest algorithm results in proper recharge of the
negative plate without creating unacceptable temperature increases. This ha
s resulted in deep-discharge lifetimes of 800 to 1000 cycles, particularly
when using a charging algorithm employing only partial recharges (97-100% r
eturn) interspersed with full conditioning recharges every 10th cycle. With
such minimal average overcharge levels, deep-cycle lifetimes approaching 1
000 cycles have been achieved without experiencing failure due to massive g
rid corrosion. (C) 2000 Elsevier Science S.A. All rights reserved.