I did some research on that a while back. I could not find any source that proved that aspirin did anything to help a battery. Rather, the best thing you can do is keep the electrolyte covering the plates but below the caps. Use only distilled water as the minerals in regular tap water could reduce the battery life. As electrolyte is sulfuric acid and water also it is difficult to see how it relates to aspirin.

All that said, hell, if it works it works.

Kitz