Charging device with an interchangeable battery for a power tool

A charging device (10, 100) of a power tool (16), comprising:

• a charging unit (12);
• and
• at least one interchangeable, rechargeable energy storage unit (14), in the form of an interchangeable battery (18), in which each energy storage unit (14) has first contact means (24) for contacting the corresponding power tool (16),
• wherein each energy storage unit (14) has additional contact means (38) for contacting the charging unit (12) in such a way that the charging unit (12) charges the energy storage unit (14) via the additional contact means (38), both when the energy storage unit (14) is connected to the power tool (16) and when the energy storage unit (14) is disconnected from the power tool (16),
• wherein each energy storage unit (14) has a sensor (44) emitting a sensor signal (S, S1, S2, S3) relating to the energy storage unit (14) and evaluated by both the power tool (16) and the charging unit (12), with each of said emitting of the sensor signal and evaluation of the sensor signal performed with a measurement procedure,
• wherein the first contact means (24) of the respective energy storage unit (14) convey the sensor signal (S, S1, S2, S3) to the power tool (16) and the additional contact means (38) convey the sensor signal (S, S1, S2, S3) to the charging unit (12), and
• wherein the power tool (16) has an evaluation and detection means (48), which detects from the sensor signal (S, S1, S2, S3) whether the charging unit (12) is currently charging the energy storage unit (14) connected to the power tool (16).