The invention relates to a connection device (10) for charging a battery device on a vehicle, having an electrical alternating current interface (20) for receiving an alternating current connector anda direct current interface (30) for receiving a direct current connector (130), wherein the direct current interface (30) has a cover flap (40) which is mounted movably between a closed position (SP)which covers the direct current interface (30) and an open position (FP) which exposes the direct current interface (30). According to the invention, the direct current interface (30) has a catch mechanism (50) with a catch means (52) on the cover flap (40), said catch means locking with a mating catch means (54) of the cover flap (40) when in the open position (FP), wherein the mating catch means (54) has an actuating section (56) with which the direct current connector (130) makes contact and which unlocks the catch device (50) when the direct current connector is received in the direct current interface (30).