This is a pack of 8 Eneloop AA Rechargeable Ni-MH Batteries from Sanyo that come pre-charged and ready to use out of the pack. They are not subject to any memory effect so you can charge them up to 1500x whether they are fully or partially drained. After one year, they maintain 90% of their charge, and after five years you'll still have 70% of the original charge. These cells have also been improved for enhanced performance in temperatures down to -4°F.