Abstract: A behind-the-ear hearing aid includes a case having an accommodating chamber, an apparatus for processing sounds, an ear hook, and a battery assembly. The apparatus is mounted in the case. The battery assembly is detachably mounted in the accommodating chamber and electrically connected to the apparatus. When the power of the battery assembly is used up, the hearing aid can be continuously used by disassembling and replacing a new battery assembly, thereby solving the problem that the battery assembly in the existing hearing aid cannot be dissembled and replaced. It is environmentally friendly and convenient for use.