SECONDARY BATTERY, BATTERY PACK, ELECTRIC VEHICLE, ELECTRIC POWER STORAGE SYSTEM, ELECTRIC POWER TOOL, AND ELECTRONIC APPARATUS

A secondary battery includes a housing member having a bent portion defining an open end, a battery element, a lid member which extends in a cross direction crossing a housing direction of the battery element to the housing member to close the open end of the housing member and has a bottom surface facing the battery element, a top surface opposite to the bottom surface, and a side surface coupled to the bottom surface and the top surface, and a sealing member interposed between the bent portion and the lid member. The bent portion includes a specific bent portion bent along each of the side surface and the top surface of the lid member. A bending ratio R (=(L/D)×100%) is 10% or more and 13% or less.