[Al Skierkiewicz]

Chris,
This is one of those myths that pass around from time to time. I think it began because lead/acid battery condition is monitored by "specific gravity" measurements. Batteries in industrial UPS power, cars and even those old deisel/electric submarines checked the batteries with this method. (The father of one of our former students actually performed this measurement on subs and told me of his daily tasks on board) This is a chemical measurement where a drop or two of battery acid is used from each cell. You'll have to look this up for a complete description.
What is real with our batteries is this... As the battery goes through repeated charge/discharge cycles, the acid (electrolyte) evaporates and vents out the top of each cell. After many cycles there is a noticeable difference in battery weight when compared to a new battery. However, when that much acid has evaporated there is less lead plates in contact with the acid and the power density and recharge time goes down. If you suspect a battery is beyond it's useful life and it is lighter than a known good battery, it's time to recycle.
Good Luck