The excess baggage charges if you carried a mobility scooter would be astronomical. Or do you imagine they'd carry it foc? I rather doubt it, they'd say bring a chair instead.
Major safety problems with carrying the battery (which is serious Dangerous Goods)) too. This may not be easy to resolve. Electric wheelchairs are a real pita to carry for this reason.
Your information is wholly inaccurate -
Mobility scooters don't attract excess baggage charges, they are transported free of charge.
Mobility scooters of all varieties can be carried easily and safely, there are procedures in place for the variety of different types of batteries/chairs.
The most important thing is that you communicate with your airline with regards to the type of chair and battery that is involved so that they can be prepared and have arranged the necessary assistance.