are rechargeable NiMH batteries that come pre-charged for immediate use. There is no memory effect and they have a very low level of self-discharge (up to 75% of nominal capacity after 12 months). are rechargeable NiMH batteries that come pre-charged for immediate use. There is no memory effect and they have a very low level of self-discharge (up to 75% of nominal capacity after 12 months). are rechargeable NiMH batteries that come pre-charged for immediate use. There is no memory effect and they have a very low level of self-discharge (up to 75% of nominal capacity after 12 months).