The Vanmoof S2 uses a proprietary li-ion battery pack, made by Darfon. Model: E4C0E Output: 36,3V 14AH/508Wh (typical) Cells: 4x10 LG 18650 cells (LGGBMJ11865)
Top and bottom caps of the enclosure are glued to a center tube with some sealant. They can be removed with mild force after removing all screws. Be sure to seal the battery pack accordingly when reassembling. When top and bottom cap of the enclosure are removed, the battery pack can be pushed out as one single part. Please be aware that the enclosure is NOT symmetrical and that mixed up contacts on the battery pack can be dangerous.
The BMS is integrated in some protective frame with the battery cells. A top cover and a protective self-adhesive plastic foil can be easyly removed, the bms circut board looks like this: (Dont mind the image artifacts with that wiring, this image is stiched from multiple photos).
The battery pack comes with a proprietary 4+7 pin connector. Exact pin configuration needs further investigation and verification, but printed markings on the bms board suggest that the pinout is as shown here:
