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In this work additives have been incorporated in the paste materials to improve the capacity and the life of the lead-acid battery. The battery's capacity is improved by additives that permanently increase the porosity of the positive active material and therefore the acid supply in the positive plate. Another material that has intrinsic conductivity was also added to permanently enhance the conductivity of the positive paste body. Antimony grids have historically given long service life at the cost of high water loss catalyzed by deposition of antimony on the negative active material, which has precluded their use in maintenance-free batteries. To combat the negative effects of antimony alloys, antimony-absorbing agents were dispersed into the negative active material to preferentially absorb and irreversibly bind the antimony ions, thereby protecting the active material. In this work we have evaluated the use of these performance-improving additives in Valve Regulated Lead Acid (VRLA) batteries. This paper is the first of a two part series; where the additives are evaluated in the Absorbed Glass Mat (AGM) type of VRLA battery where the electrolyte is immobilized in a non-woven glass mat material.The results suggest a significant improvement in battery performance through enhanced acid supply and diffusion in the positive electrode. An organic porosity additive (ES-100) and an inorganic porosity additive (ES-60) have shown an increase in active material utilization, and therefore discharge capacity, of 29% and 38% respectively at the "c" or one hour rate over similarly built additive-free Control cells. A performance advantage imparted by the porosity additives appears to be maintained throughout the life of the cells. One antimony control additive (ESA-4) appears to be showing a benefit over additive-free cells in preventing the deposition of antimony on the negative active material as evidenced by the notably altered behavior of the negative electrode. Pasting trials in a small batch mixer suggest that all of the additives are compatible with production-scale paste mixing operations used in lead-acid battery manufacturing.