Genuine Deans brand 3-pin black connector set (SET = 2 pcs). Mating connectors; 1 for Battery pack, 1 for motor/charger. Highest quality connector, for small-to-mid size amperage motor applications. Original Deans part # 1003.

The battery end (the one that is ON a battery pack) only has pins sticking out of 1 side.

The mating end (Charging end) has pins sticking out of Both sides).

Polarity (see picture, going Top to Bottom):

Black (NEG-)

Red(POS+)

Signal (or just not used).