Secondary battery

A secondary battery for an electronic appliance, comprising:

• a battery cell including a positive electrode, a negative electrode, and an electrolyte in a pack, a positive electrode terminal and a negative electrode terminal from the positive electrode and the negative electrode, respectively, being each led out from a first side face of the battery cell;
• a battery cell holder including an opening, a bottom face part, and two opposing longitudinal faces, the bottom face part being smaller than both of the opposing longitudinal faces, the battery cell being inserted into the opening, and the battery cell holder accommodating the battery cell therein such that the first side face of the battery cell is faced towards the opening;
• and
• a lid including terminal parts configured to be connected to the positive and negative electrodes upon being connected to the positive electrode terminal and the negative electrode terminal and being faced outwardly, the lid plugging the opening of the battery cell holder,
• wherein a cross section of an entirety of the secondary battery has a substantially trapezoidal flat plate shape including a long edge, a short edge that is shorter than the long edge, and opposing adjoining sides, which adjoin the long edge and the short edge, and
• wherein the positive electrode terminal and the negative electrode terminal are faced outwardly and are disposed closer to the short edge of the trapezoidal shape than to the long edge, and
• wherein the bottom face part of the battery cell holder includes one or more engagement concavities configured to receive a removable engagement member to secure the secondary battery when the secondary battery is externally attached to one of the electronic appliance and a battery charger.