Perhaps the greatest challenge you are going to have is answering the question: “Where do I put my accessories?” Some wheelchairs like the Hoveround and Go-Go chassis, there is an ample amount of room between the seat and the chassis; however some others have no room at all to add batteries, wiring or extras. So the chair itself can often dictate what you can do.
Looking for Room
For Example, The Jazzy ES or Elite series use a 4 point mount for the seat. This allows the seat to be vertically adjustable, depending on the model. However, because of this low center mount configuration, adding something under the seat… not so much. In these cases you need to look to mount a seat back system that will at least give you a power source and space for wiring and some lights.
Now Compare that to the area under the seat for these models:
The Next Option
Thinking outside the box Can help you get YOUR chair customized without needing to upgrade. Most small power wheelchairs and scooters have a place to put a basket, oxygen tank or other accessories. This is nearly a universal size and looks and works like a Reese style hitch. Now the Clever person would just use the basket as the frame, adding sides and top; then adding your batteries and wiring.