A rechargeable battery and a battery module are provided. According to embodiments, a rechargeable battery includes: an electrode assembly including a first electrode, a second electrode, and a separator; a case accommodating the electrode assembly therein and including an open side; a cap plate coupled to the open side of the case; and a terminal portion arranged on the cap plate to be electrically connected to the electrode assembly, and the terminal portion is slidable in a direction on the cap plate.