Well, the recommended charge rate for these batteries is no greater than .1C or C/10. But, that's a ball-park figure. We all charge them at the field at much higher rates, such as 1C, with field chargers, and that doesn't seem to do any short term harm. If you do this with LiPo packs, do it outside. Meanwhile, any reasonable rate of charge, as GaryHarris suggested 1 amp.. would probably work ok, but the recommended rate is no higher than C/10 or .1C.

CGr.