Batteries in hybrid electric vehicle applications operate from partial state of charge and are subjected to short periods of charge and discharge with high currents. These operating conditions create two major problems, namely low charge acceptance and progressive sulfation of the negative plates. The low specific electrochemically active surface of the negative plates can be expanded significantly by adding definite types of carbon materials, which improves substantially the charge acceptance of the battery. We assume that the slowest elementary process during charging negative plates is the dissolution of the lead sulfate crystals. This process can be accelerated by adding poly-aspartic acid (Baypure DS-100 or DS) to the negative paste or to the electrolyte. DS causes partial amorphization of the PbSO4 particles and reduces their size. Thus, the reversibility of the charge-discharge processes at the negative plates is improved and their sulfation is retarded. Besides, DS increases the overpotential of hydrogen evolution on the lead electrode. These effects of DS make it a useful additive to lead-acid batteries operated in the high-rate partial-state-of-charge duty. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.035208jes] All rights reserved.