3.8 amps@120v is certainly a short surge when first plugged in. Measure actual draw under use, I'll bet it's 1-2a.
If you want to charge it with solar or wind, you needed yet another battery bank. Let your solar panels/turbine charge their own batteries all day, then (with an inverter) use those to charge the wheelchair at night, or whenever needed. If one of these were in my plans long term, i'd probably do that. A pair of 6v golf cart batteries in series, a hundred watts of panels, and a charge controller. It would be quite useful for a lot of other things as well.
You *could* hack a 24v solar panel directly to the chair batteries, and let that charge them whenever they can be in the sun, but that makes you keep it outdoors a lot during the day.
Now, that's all long term and solar. Short term, I'd use a small generator, and call it good.