A modal antenna is formed within a battery assembly for use with a portable electronic device. In certain embodiments, the antenna is printed on an exterior surface of a battery enclosure using a conductive ink. In other embodiments, the antenna is attached, or etched, on a substrate; the substrate may at least partially include a battery housing. The antenna can include an Isolated Magnetic Dipole (IMD) antenna, or other radiating structure. Active components, such as active tuning components, are optionally included in the antenna-integrated battery assembly for the purpose of tuning the antenna.