A charging device is provided for charging an electric or hybrid vehicle from an AC power supply system. The charging device includes a supply system plug, in which charging device the supply system plug has a contact pin which is composed substantially of a first material. The charging device includes a temperature monitor. The temperature monitor has two sensor sections which are each composed substantially of a second material and which are each connected to the contact pin so that a temperature gradient within the contact pin can be detected by the temperature monitor in accordance with the principle of thermoelectric potential difference between the first material and the second material.