Battery and connection apparatus

A battery comprising:

• a casing including a concave portion and a plurality of exterior surfaces,
• the plurality of exterior surfaces including a front surface and a rear surface positioned on opposite sides of the casing, and a first side surface and a second side surface positioned on other opposite sides of the casing and orthogonal to the front surface and the rear surface;
• a connector disposed within the concave portion and including a connection terminal configured to be connected to an electrode terminal of a connection apparatus,
• wherein the concave portion includes an opening defined by a first wall portion and a second wall portion, the first wall portion is inclined towards the first side surface, the second wall portion is inclined towards the second side surface, the first wall portion and the second wall portion extend to an outermost edge of the front surface, the opening of the concave portion extends to the outermost edge of the front surface, the connection terminal is offset from the outermost edge of the front surface, and the concave portion is wider at the outermost edge of the front surface than at the connection terminal, and
• wherein the plurality of exterior surfaces of the casing further comprise a top surface and a bottom surface positioned on opposite sides of the casing and orthogonal with respect to the front surface and the first side surface, wherein a first direction extends between the front surface and the rear surface, and a second direction extends between the top surface and the bottom surface;
• and
• a guided groove that is open along the first direction and into the second side surface, wherein the guided groove includes an upper face that is disposed a different distance from the bottom surface than a middle portion face of the concave portion.