You can just go ahead and charge, no need to discharge. If you are using the charger that came with the equipment, just charge for at least 14 to 16 hours (treat it as a new unit would be treated). You might want to check out
www.rcbatteryclinic.com for some good info on how to care for your batteries. You get a lot of bad or downright missleading info here on the discussion board, i.e. like NiCads have a memory problem (totaly false) and need to be completely discharged before charging (again totaly false). If you are in doubt, contact the battery manufacturer for good info.