A modular canal hearing aid assembly having a main module and a disposable battery module that docks perpendicularly into the main module which surrounds the battery module circumferentially and laterally for secure connection that eliminates inadvertent separation of the modules during removal of the hearing aid assembly from the ear canal. The disposable battery module incorporates battery cell, sound port, and handle, in a unitary structure that is easy to handle and replace as an integrated unit when any of the degradables within are consumed. The disposable battery module also comprises a membrane filter for filtering out earwax and liquids. The perpendicular docking mechanism provides highly space efficient design for comfortable and inconspicuous fit deep in the ear canal.