Additives in the negative active-material of lead–acid batteries were examined to determine whether they could prevent progressive accumulation of lead sulfate (PbSO4) in negative plates during high-rate partial-state-of-charge (HRPSoC) operation. This phenomenon is caused by progressive growth of PbSO4 particles and a lack of conductive paths near these PbSO4 particles. Barium sulfate (BaSO4) particles in various sizes and synthetic lignin were added to the negative active-material to control PbSO4 particle size during HRPSoC cycle-life. Some types of carbon fibres were also added to form conductive paths around the PbSO4 particles. Synthetic lignin was found to be the most effective additive for improving battery life in HRPSoC cycle-life tests, whereas the other factors such as BaSO4 size or carbon fibre extended less influence. The growth rate of PbSO4 particles per cycle was much lower in a cell with synthetic lignin than in a cell with natural lignin.