Single-module cycle life of the Horizon® valve-regulated lead-acid battery has been limited principally by the growth of the negative electrode edges. Left unchecked in the first-generation Horizon® design, this anode growth contacts the positive electrode in a contiguous cell, shorting the cells, and prematurely ending battery life. In the current Horizon® design, Electrosource has modified the module plenum with an intercellular insulator, which interdicts anode edge growth and moves the end-of-life mechanism to the cathode. This modification approximately doubles Horizon® cycle life to greater than 700 cycles (C/ 1 to 80% DOD) and improves robustness of the battery significantly. Test data for the improved design are presented.