I feel sorry for your bike, embarrassing it like that. No bike of mine has ridden on or in a gasser since LFP came down for a visit 9 years ago, when none of mine had enough range to reach the beach. It's time to step up and build some electric transportation, not just toys. It sounds like you need a big batteried emoto capable of hauling a trailer carrying your offroad ebike. Then you can quick charge the offroader from the big battery bank of the 2 or 3 wheeler. I like the 3 wheeler for that use to go really big with the battery, and to be more stable in the wind with a large solar panel top with foldout extensions while parked for shade and useful amounts of power.
If I'm understanding the charge through the motor and controller thing of the Nucs, it gives me a way to charge for almost any DC source, even another battery of any voltage and the controller limits the current and max voltage.