1. An electricity storage unit comprising:an electricity storage device; a circuit portion on which an electronic component is mounted;
a heat dissipation member that dissipates heat from the circuit portion; and
a holding member that holds the electricity storage device in a state where the electricity storage device, the circuit portion, and the heat dissipation member are stacked such that the circuit portion is located between the electricity storage device and the heat dissipation member,
wherein the holding member includes a pair of opposing inner walls, the each of the pair of opposing inner walls having a supporting portion, the supporting portion having a distal end opposite a proximal end, the distal end abuts against the heat dissipation member, and
a partition wall portion being a planar member extending between the pair of opposing inner walls of the holding member and interconnected to the proximal end of each of the supporting portion so as to be elevated above the circuit portion, the supporting portion bounding a peripheral edge of the partition wall, the partition wall portion having a top surface opposite of a bottom surface, wherein the electricity storage device is placed on the top surface of the partition wall portion and the bottom surface of the partition wall portion is spaced apart from and faces the circuit portion forming a gap therebetween so as to be clear of the circuit portion.