Search for an optimized cyclic charging algorithm for valve-regulated lead-acid batteries

Valve-regulated lead-acid (VRLA) batteries are characterized by relatively poor performance in cyclic applications of the order of two hundred to three 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 recombination 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 where, traditionally, low currents and low overcharge limits have been employed 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 has resulted in deep-discharge lifetimes of 800 to 1000 cycles, particularly when using a charging algorithm employing only partial recharges (97-100% return) interspersed with full conditioning recharges every 10th cycle. With such minimal average overcharge levels, deep-cycle lifetimes approaching 1000 cycles have been achieved without experiencing failure due to massive grid corrosion. (C) 2000 Elsevier Science S.A. All rights reserved.