Abstract: A battery pack for powering an electrical device, comprising: a housing for a plurality of electrochemical cells, each having an elongate body with terminals at either end thereof; and electrical circuitry for coupling in series or parallel the plurality of electrochemical cells in the housing to electrical contacts of the electrical device; wherein the housing comprises: a first part having a body defining a chamber with an opening, the body being configured to retain the plurality of electrochemical cells side by side in the chamber, with one terminal of each cell facing towards the opening; and a second part comprising a filter and at least one vent, with the second part being configured to cover the opening of the chamber when coupled to the first part such that any combustion gases generated in the chamber by electrochemical cell malfunction pass through the opening and the filter before being vented externally of the housing through the at least one vent.