My string trimmer runs on a rechargeable NiCd battery. It's only two
years old but doesn't hold much of a charge anymore. The trimmer
manufacturer's tech support suggested that I may be able to bring it
back to life by discharging the battery completely, charging it for
six hours, and repeating this cycle three times, only charging it for
one hour the final time. After each of the charges, when I attached a
clamp to the trimmer's switch to let it run so it would discharge, it
certainly did seem to have plenty of power. But after doing this
process, when I went to actually use it, the trimmer barely had enough
juice to spin even though I had left the battery on the charger for
several days after doing the cycling process.

Does this technique of bringing a NiCd battery back to life work?
Once I charge a NiCd, can I leave it in the charger until its next use
or must I take it off the charger after a certain time? Do I have to
discharge the battery completely before recharging it every time I use
the trimmer?