You should treat a battery that has been stored (or not used for a long time) just as you would a new battery. Do a forming charge, that is a slow charge at approximately 0.1C for 15 to 16 hours. It may take two or three cycles of this forming charge followed by a discharge to about 1 volt/cell at 0.25C to bring the battery back to full capacity. Check out www.rcbatteryclinic.com for some good info on how to care for your batteries.