When all else fails, try the dictionary:
Mobile: 1: capable of moving or being moved; 5: marked by the use of vehicles for transportation
Portable: 1a : capable of being carried or moved about; 1c : usable on many computers with little or no modification
Mobile and Portable are also listed as synonyms for each other.
Portable seems to imply that it can be carried by a person. The Latin origin meant to carry.
Mobile simply means movable, by whatever means necessary. The Latin origin simply means to move. Extremes are a mobile phone, which can be carried to a mobile rocket launcher or M.A.S.H. unit (Mobile Army Surgical Hospital), which require trucks to move.
So portable always meant mobile, but mobile did not always mean portable. However, modern usage tends to get sloppy, so there may no longer be a true distinction.