I was skeptical when I saw this, but I figured what the heck and gave it a try. Fixed two completely dead 18V DeWalt drill batteries - they now hold a charge for about 45 minutes of use (new they gave just under an hour).

Explanation (via http://ysuusy.com/easybatteryfix.html):

"Over time the crystals within a NiCd cell begin to combine and get larger. This causes them to loose capacitance and also break through the inner seals of the cell. Surging the NiCd cell using a higher voltage causes the crystals within the NiCd cell to shatter and become smaller. These smaller crystals have a greater surface area and therefore contain a greater capacitance for energy."

ya, this fix has been around a long time (came out for cell phone batteries back when cell phones used NiCad). FYI, the fix does not last, after a few charge cycles back to being dead. :(