Appendix 2: POWER UNIT SYSTEMS, FUNCTIONS AND COMPONENTS is the place to look.
ES parts defined in Article 5.4.3 is included in Article 5.22: Replacing power unit parts
ES excluding parts defined in Article 5.4.3 is not included in Article 5.22: Replacing power unit parts
The ES components (both those defined by 5.4.3 and those that are not) are exluded from articles 5.4.1: Weight and 5.4.2: Centre of Gravity.
5.4.1 The overall weight of the power unit must be a minimum of 145kg.
5.4.2 The centre of gravity of the power unit may not lie less than 200mm above the reference plane.
5.4.3 The total weight of the part of the ES that stores energy, i.e. the cells (including any clamping plates) and electrical connections between cells, must be no less than 20kg and must not exceed 25kg.
So, to clarify, the storage parts of the ES are part of the sealed power unit (one of the modules), but other items, such as wires (edit: wires not connecting to cells, but to the control units or MGUs), cooling circuits, etc, are not.
No part of the ES is counted towards the weight of the Power Unit or to the calculation of its centre of gravity.