No memory effect. Can be charged or discharged as needed without loss of capacity.
Compatible with replacement Black&Decker 18v power tools:FS18HV, FS18ID, FS18PS HPB18 HPB18-OPE 244760-00
The third prong (temp. sensor) enables fast charge mode (approx. 3 amps instead of 1amp; full charge in about an hour or less) . The exposed metal square is for temp sensor on generic chargers.
30 days money back, 1 Year warranty and friendly customer service, the batteries are CE certified and OEM products tested.