A power supply system for a portable electronic device is disclosed. The power supply system includes a number of battery cells distributed between a number of structural support members of a housing of the portable electronic device. The battery cells of the power supply can be separated so that they can be individually installed between the structural support members of the housing. After installing the battery cells a battery busbar of the power supply system can be subsequently slid through openings defined by the structural support members so that the battery busbar can electrically couple together battery cells separated by structural support members. The battery busbar can also be electrically coupled to a battery management unit of the power supply system, which can also be separated from the battery cells by a structural support member.