A battery pack includes a plurality of unit batteries arranged side by side in a first direction, each unit battery including a can accommodating an opening including an electrode assembly having a first electrode plate, a second electrode plate, and a separator between the electrode plates, and a cap plate sealing the opening. The plurality of unit batteries may be arranged side by side in the first direction with all the cap plates exposed in the same direction. The battery pack may further include a protection circuit module adjacent to the cap plate with a circuit board extending in the first direction and a protection device coupled to it, wherein each unit battery further includes a first terminal on a first area of the cap plate and a second terminal on a second area of the cap plate, each coupled to the unit battery and the protection circuit module.