This disclosure relates to compositions and methods for improving the performance of batteries, such as lead-acid batteries, including reviving or rejuvenating a partially or totally dead battery, by adding an amount of nonionic, ground state metal nanoparticles to the electrolyte of the battery, and optionally recharging the battery by applying a voltage. The metal nanoparticles may be gold and coral-shaped and are added to provide a concentration within the electrolyte of 100 ppb to 2 ppm or more (e.g., up to 5 ppm, 10 ppm, 25 ppm, 50 ppm, or 100 ppm). The metal nanoparticles may be added to battery electrode paste applied to the electrodes to enhance newly manufactured or remanufactured batteries.