Final Update: So, I plugged in the trickle charger at noon and decided to give it a few hours to see if it would go up from 10.7v. It didn't. Obviously, I could run it through de-sulfation again. However, given the fact that it so quickly went back down to 8v while on the trickle charger, I think there's something else going on with the battery, whether the cells changed their compositional properties or something is wrong with the acid solution. Either way, even if I was able to briefly get it back to 13.1v, if it won't reliably stay at 13.1v, it's not worth a plugged nickel to me. Maybe de-sulfation will give more reliable results to individuals in cooler climates. But, based on my own experience, de-sulfation appears to be a fruitless endeavor for anyone who lives in an environment that stays over 90F at least 1/3rd of the year. If you live someplace like Texas, Arizona, or New Mexico, don't expect your lead-acid car battery to last any more than 6 years.