The effect of polyaspartate (PASP) on the performance of the lead-acid negative plate has been investigated. It was established that this polymer additive controls the crystallization process of lead sulphate and modifies the shape and size of PbSO4 crystals. The addition of PASP to the negative paste and to the electrolyte improves the utilization of the negative active material and reduces the internal resistance of the negative plates. The results obtained during cycling of lead-acid cells under simple simulated HRPSoC cycling duty with 2C discharge current show that addition of PASP improves the cycling ability of the negative plates and thus decreases the frequency of equalization charging during operation. A beneficial effect on the performance of lead-acid batteries was observed during HRPSoC cycling of flooded batteries with 0.1% PASP in the electrolyte. The addition of PASP leads to formation of smaller PbSO4 crystals, which are more easily reduced during charge and hence prevents the accumulation of large lead sulphate crystals on the negative plates in HRPSoC duty.