In this paper, we investigate the use of paste additives to improve the performance of a horizontal plate, lead–acid battery. The horizontal plate battery can deliver high power for electric and hybrid electric vehicle applications. We develop a series of designs having different paste additives to continuously improve the specific energy (W h/kg) performance of this battery. Computer models, previously developed and reported, are used to estimate the specific energy performance of these designs. The baseline, horizontal plate battery containing no additives has a specific energy of 30–35 W h/kg. The final design in our design progression uses both porous and conductive paste additives to provide an estimated specific energy of 60–70 W h/kg.