Battery and connection apparatus

A battery, comprising:

• a casing configured to house at least one battery cell, the casing including a front surface and a rear surface spaced apart along a longitudinal direction, a first side surface and a second side surface spaced apart along a widthwise direction orthogonal to the longitudinal direction, and a bottom surface and a top surface spaced apart along a height direction orthogonal to the longitudinal and the widthwise direction;
• a terminal part including a connection terminal configured to connect to an electrode terminal of a connection apparatus, the connection terminal including a front face proximate the front surface of the casing;
• a first functional groove and a second functional groove;
• and
• a concave portion having an opening defined by a first wall portion and a second wall portion, the first wall portion extending towards the first side surface, the second wall portion extending towards the second side surface, the concave portion including a middle portion face extending between the first wall portion and the second wall portion in the widthwise direction, wherein
• the first functional groove is located between the first side surface and the terminal part,
• the second functional groove is located between the second side surface and the terminal part,
• the first functional groove includes a first functional unit and a second functional unit, the first functional unit and the second functional unit of the first functional groove being respective first and second rectangular shaped portions of the first functional groove,
• the first functional unit and the second functional unit of the first functional groove extend in the longitudinal direction towards the rear surface, the first functional unit extending a different distance towards the rear surface than the second functional unit,
• the second functional groove includes a first functional unit and a second functional unit, the first functional unit and the second functional unit of the second functional groove being respective first and second rectangular shaped portions of the second functional groove,
• the first functional unit and the second functional unit of the second functional groove extend in the longitudinal direction towards the rear surface, the first functional unit extending a different distance towards the rear surface than the second functional unit,
• the first functional unit and the second functional unit of the first functional groove mirror the first functional unit and the second functional unit of the second functional groove about an axis along the longitudinal direction, and
• the first wall portion and the second wall portion of the concave portion respectively extend from the front surface to the terminal part without extending past the terminal part in the longitudinal direction.